For the reasons outlined above. Occam's razor + locality.

if I stand a needle on it's tip on a glass plate, will needle remain standing indefinitely? No it probably won't even though by Occam's razor, zero deviation from vertical is (arguably) more probable than any other specific deviation from vertical. MWI seems to require exact linearity, and QM and QFT don't do gravity, i.e. are approximate. Linear is a first order approximation to nearly anything.

None of the "easy stuff" is pertinent to the argument that MWI is more probable than straw-Copenhagen.

Intelligence and careful thinking --> getting easy stuff right and maybe (very rarely) getting hard stuff right.

Lack of intelligence and/or careful thinking --> getting easy stuff wrong and getting hard stuff certainly wrong.

What is straw Copenhagen anyway? Objective collapse caused by consciousness? Copenhagen is not objective collapse. It is a theory for predicting and modelling the observations. With the MWI you still need to single out one observer, because something happens in real world that does single out one observer, as anyone can readily attest, and so there's no actual difference here in any math, it's only a difference in how you look at this math.

edit: ghahahahaha, wait, you literally think it has higher probability? (i seen another of the Yudkowsky's comments where he said something about his better understanding of probability theory) Well, here's the bullet: the probability of our reality being quantum mechanics or quantum field theory, within platonic space, is 0 (basically, vanishingly small, predicated on the experiments confirming general relativity all failing), because gravity exists and works so and so but that's not part of QFT. 0 times anything is still 0. (That doesn't mean the probability of alternate realities is 0, if there can be such a thing)