IRS receives about 25 million returns each year with Schedule C.  They receive less than 2 million with Schedule F.  That's out of about 150 million total returns (not counting those this year from "nonfilers.")  Providing a feature that may be useful for 15% of returns, may be useful.  Providing one for less than 2% of returns, raises the question of whether those of us who would not use it should pay for those who do.

The same situation applies to state returns.  The two-year comparison is offered for California, where 18 million returns are filed.  It's not for Arizona, with only 3 million.  

Of course, I may use the two-year comparison on only 15% of the returns I prepare (in my case, it's probably less than 10%), but for those returns it can be very helpful for spotting errors or omissions. But I could do the same, looking at a paper copy of last year's return.  I have only one Schedule F filer, 50% fewer than I did a couple years ago, and I don't want to pay more for bells and whistles that I might use only once a year.