Nah, it has nothing to do with the emissions regulations, especially considering we have some of the most lax regulations in the developed world. Honda decided long ago to push hybrids more in this country since American buyers were so anti-diesel. They don't sell diesels because it would detract from hybrid sales. In Europe, where diesels are commonplace, they can open a hybrid segment as well, and the only thing the sales of hybrids will affect will be the sales of the standard models, which doesn't bother Honda in the slightest, since they make more off hybrids and diesels. Switching away from diesels to follow a gas or hybrid only sales model in Europe would just lose them sales. Adding a diesel option in the US would not gain them a significant number of sales and would hurt their margins for hybrids. Plus, diesel sales in the US probably wouldn't be high enough for a few years, so they would be losing a lot of money keeping inventories.
Even VW had to take a couple of years off from the U.S. market when its TDI couldn't meet the new emissions regulations. That came at the time when only VW and Mercedes had diesel passenger cars in the U.S. Now, VW is back, BMW is back (for now), Chevy is on its way, and there should be more to come.
Personally, I like diesels. I would like to see more of them. I am sure that automakers want to cash in on the hybrid buzz as well, but the emissions regs have a lot to do with it. Nissan was going to bring over a diesel Maxima in 2008 or 2009, but cancelled (I used to work for Nissan). Honda was going to bring the 2.2 diesel over for the 2009 Accord, but cancelled (I worked for Honda after Nissan).
Since when did VW have a problem meeting our regulations? Unless you are talking about the 80s, when we had a bunch of really odd rules in place. As for Nissan.... well, whether or not you worked for them, our emissions regulations are far more lenient than what you will find anywhere in the EU or in Japan. Even California's emissions regulations are more lenient than what you find in many parts of the world. Seriously... Have you ever looked at the emissions regulations in Japan? To sell a car here, they do a couple extra crash tests, put on crappier headlights, tune for lower octane and slightly dirtier emissions to get a couple more ponies and mpg.
Either way, the official statements by almost EVERY car company that has been asked why they don't introduce any of their small diesels that they sell overseas in the US has been that they are following a hybrid only strategy in the US, due to the popularity of hybrids in America, and because they work well in our market, since diesel is not available at every gas station, unlike in other countries. Either that, or they are so invested in their advanced gas engine technology. Mazda is pushing skyactiv, Toyota seems to want to phase out non-hybrids all together, Nissan went towards pushing their full electric towards our market instead of gambling on a diesel that would have sold in even smaller numbers than the worst case scenario for their full electric, and everyone else is doing something similar. Heck, they aren't wrong either. That is what the consumers here want. They want things like the Prius, Volt, Leaf or things like ecoboost.
Seriously though, can anyone think of a single diesel car in America that is REALLY mainstream? Look at the Jetta, Passat and Beetle for instance. Compare the numbers of each that run on gas to the number that run on diesel. It is a wonder they continue to offer diesel engines for the American market. Government isn't the reason we don't have small diesel engines here in the US. GM is for converting a small block to diesel by just plugging the hole for the spark plug, along with a majority of the public who think like my mother when I tried to convince her to get a diesel Passat instead of her Focus. "But I don't like the sound diesels make and diesels smell bad. Your uncle has that GMC and it is so loud and it smokes and if I had something like that the neighbors would think I was a trashy person. Plus, after growing up on the farm, I had enough of diesel tractors and Semis" Heck, I couldn't even convince her to take the time to go look at one to see that small diesels are an entirely different animal. It is for exactly the same reason you see so few cars that come with a manual transmission these days. The percentage of buyers who would actually option them are so low, it would cost too much to make it available. Only in this case, you have an option that adds a significant cost to purchasing the vehicle, which would scare off even more customers, despite the fact that you would pay for that option within a couple years of ownership.
To sum it up, the answers range from, "Diesels are MUCH less efficient than gas engines" from a claimed auto mechanic, to, "Gas engines have more power, are more efficient and more reliable." Of course, there are a few, "they are hard to start." and most replies involve the "Diesel costs more."
Since when did VW have a problem meeting our regulations?
They didn't call it a problem, but more of a "we don't plan to make a compliant diesel right away" when diesel emission regs were toughened. It was in 2005 or 2006. VW had stock piled previous MY TDI's for sale during the next year until the the compliant engine was available.
Some of those yahoo answers replies are ignorant. Which goes to show why diesels aren't popular here. The belief that they haven't improved over the diesel cars of twenty to thirty years ago that have left a bad impression on the public consciousness. With the only diesels available in the intervening time being oversized blocks in HD trucks, some of which owners had purposely billowing smoke, and in high priced cars of questionable brand reliability, didn't help the perception.
Fuel costs and smell are the only cons actually based in today's reality.
Efficiency did drop with the introduction of emission controls. That also happened with gassers, and the experience there has let the manufacturers improve emission controls for efficiency at a faster rate. Systems that don't make use of urea injection take a heavier hit to fuel economy than ones that do. With urea being an unknown to the public, and reports of Mercedes charging $100+ for a refill, Honda went the non-urea route with the planned Accord, and it probably didn't do as well as they hoped on the EPA tests.
Now, VW is back, BMW is back (for now), Chevy is on its way, and there should be more to come.
Mazda's Skyactiv suite also includes a low compression diesel. With tightening emission regulations on diesels overseas, the only hurdle to not bring diesels over for all companies is the public perception of the past engines.