There's no serious threat of another club coming to poach him, right? Even if we won several league titles and the CL, I can't imagine Mikel leaving before 2027. I assume that this is being done with the same idea behind giving key/star players improved contracts prematurely as a show of faith.
I've learned the hard way to never trust the likes of Barcelona. And I think the club owners have too. Mikel cleary loves Arsenal deeply. But he's also floated the idea of eventually moving back to Spain (which fuels the likes of Barcelona to contemplate periodically trying to poach him).
Hopefully money + love talks and we can keep hold of him for 10+ years. Would be wonderful if he pulled an Arsene and stayed with us for 20+ years (as long as he's still doing a good job, obviously).
arteta has ranked ancelotti above wenger in interviews solely because the former has repeated his success in different leagues and different conditions. it's evident that arteta values this diversity of experience more than that of building a legacy.
i would wager that he'll look to move on once he achieves one PL and one CL trophy each at the soon-to-be-named arsene wenger arena.