Looks like you just have a ton of fuel-ups marked as partial. Whenever you do that, Fuelly doesn't calculate an individual MPG for that tank or the next one. Here's more info in the FAQ about partial fuel-ups. Keep in mind those fuel-ups do contribute to your average MPG, and that's being calculated.
Yes, when you've got a 35 gallon tank that $75 fillup max gets reached pretty quick. I was under the impression that when I was able to fill the tank it would populate all the empty mpg fields prior to that.