The copyright holder (the author) is solely responsible for choosing how they want their work to be distributed, and is not bound by any other sort of constraint. They can choose any license at any time, and change their mind however often, and it whatever direction they want. Any previous licenses used (MIT here) bear no effect whatsoever. There is no license in the world (and cannot be) that would prohibit the copyright owner from changing it. It makes no sense, the license terms only apply to the licensee, not to the licensor.

Of course, the author cannot retroactively change the license of any previously distributed work. Anyone is free to fork off Bear from its last MIT code and do whatever they want with it.

So no, the MIT license does not "explicitly allow to relicense a project at any point" (emphasis mine). The MIT license allows licensees to license their derived work however they see fit, it has no effect on the relicensing by the licensor (the copyright holder).