It's not a case of lack of effort. They tried and tried for years. They grew up idolising Gerrard and Henry with dreams of paving out similar careers. Both were mature for their age and came from good families with footballing backgrounds. They never went off the rails and started partying too much or stopped paying attention to their fitness. From what I heard, these two were focused on football and I could always see that on the pitch. Never an attitude problem with either. Effort can only get you so far. See Danny Welbeck.
To look at Wenger's treatment of a player like Lacazette or Perez and see how that can damage confidence but not see similarities in what he did with Walcott and Ox is what I find strange when it comes to Arsenal fans. Early on in their careers, both players would either get left out of major games after a good performance or hooked after 60 minutes despite playing well. That's enough to mess with the confidence of a young player. Then think about the injuries and how that effects the players confidence.
In Theo's case, he had major surgery on both shoulders and that effected his game. He adjusted and spent less time on the ball and focused more on off the ball runs because I don't think his body could take the physical punishment. Or at least I believe that was what he was advised. When you hear Wenger say he has told Theo to study Freddie Ljunberg, along with the ridiculous comparisons to Messi, saying Theo's off the ball movement is better than Messi's, it became clear to me that Wenger was trying to develop Theo into a 'wide forward'. It's a term he's use a lot to describe Theo. He stopped being a winger. I remember Wenger once saying Theo was struggling to score goals and be as effective in attack because he's using a lot of energy tracking back to defend.
When Wenger publicly question Theo's defensive ability, we saw another change in Theo's game where he actually proved he could defend and score goals. That was his last full season for us at Arsenal before being left on the bench and then sold to Everton.
Ox was wise to move on after seeing all this. Wenger wanted to push him to playing as a wing back. Why the heck would you trust him to do that when he can't even develop a natural wingback like Bellerin?