I think at least some of it is that other teams have taken notice of him and are making sure to counter him. He's not under the radar anymore. He has to figure out how to deal with the extra attention he's getting from opponents.
I think this happens to a lot of young players.
Yeah, but it's easier to make adjustments when you aren't on top. Any change will probably improve Everton. It's much harder when you've been dominating. Much more likely to upset the balance.