Why is Will Howard not considered a good NFL prospect?

I don't understand football well enough to evaluate college players. It does seem to me that NFL teams have a difficult time with this as well. Howard has NFL size, IMO. He has a good arm. His accuracy was excellent this year. He showed his ability scramble. He was throwing to NFL caliber receivers, but that's the quality he would be throwing to in the NFL. I thought he showed good poise overall. I just don't understand why he isn't talked about at all.

What is he missing?