Personally always really liked Welbeck, but my theory is that he felt he had more chances of playing at Arsenal and wanted out. I think it's a shame he went, because with a little more patience he could've stayed with us for years. We could've used him for sure even if he doesn't score that much. And now he's pretty much in the same boat at Arsenal, but with Giroud/Walcott types it's maybe a bit easier to get games than competing big names like Rooney/RVP/Di Maria. Can't really blame him for being impatient, and can't really blame the club for letting him go. You just knew he was going to score yesterday, but that's football.
Has the video of his first interview at Arsenal been posted a lot? He seems really happy, and within 20 seconds he talks about how he "envisioned himself playing at Arsenal before", which says enough about his vision on his career I think, like almost 95% of the players out there he's interested in himself first.