Palmer to Chelsea is a weird one. He's been getting more and more game time for City and has scored a couple of big goals for them recently. I suppose he felt the signing of Doku meant that his chances would descrease again. I think there's a very good player there from what I've seen of him, but never thought for a moment he would end up at Chelsea.
Palmer is probably looking at Foden who is a generational talent; even if he's a twat and I think that terms is overused, it does apply here imho. It took years of slowly getting more and more game time for Pep to fully trust him. Not sure it's even the case now!