There's 2 things going on here:
1) I love John Wall. When healthy he's a 20 and 10, game changing, franchise player. He's a highlight reel every game, making unbelievable plays on both sides of the ball. An expert of the chase-down block. But unfortunately, he hasn't been able to stay healthy. He hasn't played a full season since 2016-017 and missed the entirety of this last season. While he was part of the Wizards, there were constant rumors that him and Bradley Beal didn't get along. The rumors were often denied, but Beal flourished last season without Wall as his counterpart.
2) Wall's contract is MASSIVE and might be incredibly hard to trade. Right before getting hurt he signed a 4 year, $170 million deal. He might have to play to prove to possible trade candidates that he's 100% healthy. Teams will not be keen on trading for Wall sight unseen, and you can't blame them.
It might be in the best interest for both Washington and Wall to move on. Which is unfortunate because there is a pretty good squad brewing in DC, with Beal, Rui, Bertans who signed a new 5 year deal today, Thomas Bryant, and an emerging Troy Brown Jr. I think if Wall settled down he'd realize he has a pretty good supporting cast around him, but it appears he is uninterested in such things.
Is Wall for Westbrook still alive? Makes more sense now, if Russ is cool with coming to DC, I'm sure Wall wouldn't mind going to Houston. But I will say again, I wouldn't be shocked if he's not tradable until he plays, which could make things weird, but I don't know if there's any other choice.