No reason at all.
You've developed amnesia. Taysom turned a big corner as a junior, and until he got hurt at Nebraska was playing very well.
I get sick of people blathering about "progressions" when they clearly don't have the first clue what they're talking about. Anybody who knows what they're looking at and for can see that Taysom makes reads and finds the right guy just fine. No qb is going to do it right every time.
You state things like WRs dropping balls and the line playing poorly and then go straight to "but." Well, sir, those are the reasons many quarterbacks fail to produce: they're given a vehicle with a seized motor and asked to drive it.