I'm speculating that the prevailing wisdom among the upper levels of management (and ownership) in the NFL is that you are still better off with a prototypical pocket passer (read white) as opposed to some of the more athletic modern style quarterbacks (read black). Or at the very least it's a safer pick.
I personally feel that Russell Wilson has probably had a huge influence in helping to change this over the past few years. But I think the train of thought still exists. There's probably a confirmation bias going on, where people look to the JaMarcus Russell's and EJ Manuel's as evidence of "athleticism" being overvalued.
Even just looking at guys like Patrick Mahomes and Lamar Jackson, both had question marks about the ability of their skills translating to the NFL. No one ever thinks about how a player can change the position but rather how they will have to change and adapt to the NFL.
This article here sums up what I believe a lot of decision making people feel:
Russell Wilson, MVP candidate, strengths and weaknesses | SI.com