Because it’s only six more months...
If he stays here until the end of the season he’ll get 25ish goals and his stock will continue to rise. There is absolutely no risk for him staying and at 21, there’s no rush.
Leaving is a huge risk for him. Wolves may not even start him, or he may find it difficult as he did last year. If that’s the case, he’s back to square one again next season and would likely find himself at a Championship or lower Premier League club at best. Stay and get more goals means he will improve as a player and may get a big move in the summer.
The sensible thing to do is stay, then move to pastures new in the summer (or stay at Chelsea). But he may back himself to do it in the league above from now, which I feel isn’t worth the risk at this stage and he may as well wait a few months.