If you expected great things from Bo when he made it to Raw I don't know what to tell you. Raw and NXT serve different masters. New guys generally get pushes and then get pushed down. Few get to really showcase their stuff until they really get over. Dallas never did. He exceeded my expectations for him in his short time before his injury but it was mostly with his comedy.
But the answer to your question is mostly his injury but also that he is not that talented as a professional wrestler.
I agree with most of what you said here, including the part in bold. The thing is, that is a BS catch 22 from WWE. You get TV time when you start getting over, well how do you get over without it?
When the fan base at large doesn't watch NXT a lot of the momentum doesn't transfer over, which is why you have to give them some time for the audience to get acclimated.
Adrian Neville is the perfect example so far…he wrestled a Raw match a few months back, made his official debut at the Raw after WM, which has a VERY smart crowd, so they are of course super familiar with him, and to the audience at home it makes him come across as larger than life to see the reaction he got. Then he has a match that he gets to shine in. Week 1=A+
Tonight, he gets a singles match, against the WWE champion, didn't expect him to win, but still a good showing against a top guy. Week 2=A+
That is how you debut NXT talent. Bo got TV time, but not enough for his momentum to really pick up steam, and see where he could go. I would've put the IC belt on him, and let it roll from there.
As far as him not being a great wrestler, I agree he's not the best, but as "sports entertainment" seems more and more to supersede wrestling ability, as long as you're adequate in the ring that seems to be enough. Hell, they thought Miz was good enough to hold (and retain!) the WWE title, and main event a WM with it, and that was 4 years ago! If he could do it, I'm not sure what they think Bo is lacking.