I think part of it is that he looks small. I'm interested to see what his numbers are at Pro Day. You're right though,
there's never been a better time for shorter QB's to succeed. However, they're the exception, not the rule. Kyler Murray is an elite athlete. Russel Wilson throws the best deep ball in the game and is honestly a modern day Steve Young. Drew Brees is one of the smartest, most accurate QB's of all time. They succeed despite being small, not because they're small. They've had to overcome their size with something elite. If you asked a scout what they prefer, they would all say the typical 6'5" QB (assuming, of course, everything else equal). I think that's part of the reason why Lawrence is such a good prospect. He can move really well and he's got the elite size.