Look a bit harder and the quotes are there. Phil Neville, Holloway and Southgate have all spoke about it.
He apparently had a free reign at Crystal Palace and just turned up when he felt like it to training, was late for games etc. Just watching him frequently berate teammates at youth level was enough evidence.
Just looked it up, you're very negative if you took that out of it. Phil Neville has primarly spoken about him not having acclamatised to the United life, how different it is and what it costs, saying that multiple have struggled with it like Evra, Vidic, Marouane, fair enough.
Holloway reviewed Zaha's period at United, and when he came to the topic that Zaha turned up late, he said that's not how he knows Zaha and that's nothing like Zaha would do, he seemed surprised, so I'd rather take it as an incident/fault than evidence of his shit attitude. Not really found something from Southgate, bar saying he should step up and talking about the Morrison row, that it's fine and that is happens sometimes.
Or you're being way too dramatic, or I'm not searching good enough, but I doubt Zaha has a shit attitude, rather think he just wasnt ready for it.