But why should the probability for lower-complexity hypotheses be any lower?
It shouldn’t, it should be higher.
If you just meant ”… be any higher?” then the answer is that if the probabilities of the higher-complexity hypotheses tend to zero, then for any particular low-complexity hypothesis H all but finitely many of the higher-complexity hypotheses have lower probability. (That’s just part of what “tending to zero” means.)
But why should the probability for lower-complexity hypotheses be any lower?
It shouldn’t, it should be higher.
If you just meant ”… be any higher?” then the answer is that if the probabilities of the higher-complexity hypotheses tend to zero, then for any particular low-complexity hypothesis H all but finitely many of the higher-complexity hypotheses have lower probability. (That’s just part of what “tending to zero” means.)