I don't doubt his ability. It's clear he has top 5 talent in this draft. And he may turn out to be a great player. But if I have my pick of players that early in the draft, I'm not choosing the one with SEVERAL red flags, even if I'm giving up a little bit in talent in picking someone else who doesn't. Drafting players is hard enough to get right as it is, why take such an obvious risk so early in the draft (in this hypothetical situation)? Seems like a very easy "pass" to me, especially when he doesn't even fit a lot of the Jazz's specific needs (defensively particularly).
Here's an in-depth look at Cousins vs Favors.
https://evilcowtowninc.wordpress.com/2010/04/24/demarcus-cousins-vs-derrick-favors/
Yet another red flag is Cousins' shooting ability. "In eFG%, Favors is 28th in the entire country. In TS%, Favors is 61st. Cousins is not even in the top 400 in either category."