The Oilers have tried to fill the staff with people close to McDavid. That could be because he's been unhappy with how the team has been run by those at the top (understandably at times). Either he is happy with the situation now his people are there or he's very frustrated and has seriously considered going.
He'll get another $120m easily over the next decade wherever he signs, so it is a matter of where is the best place for him to win a cup. $5m-$10m is a lot of money but is it better than winning a cup when you've got $220m+ in the bank anyway.
The Draisaitl deal was thought of as helping keep McDavid, but if you're McDavid you have the comfort that you know the franchise still has an elite player even if you leave.