Taijuan Walker is a young controllable pitcher and was a top pitching prospect for a very long time, he's also having a pretty decent year, something seemed to click after a rough start and he's been excellent ever since. This is why, like RJF has said, he's not getting traded any time soon. When teams start selling off their main assets they don't go for the 22 year old with a lot of potential and under team control.
Ironically, that last sentence also applies to Daniel Norris perfectly.