SecularFrummy: Hashem would make an alternative to allow for bechirah. The Ramban writes extensively about the fact that if there were no bechirah, there could be no reward. If miracles were completely obvious, and you had to believe in them, it wouldn’t be a big deal to believe in Hashem. The fact that there is a plausible explanation means the belief can be rewarded.
I don’t know what people thought a few hundred years ago. Maybe Hashem arranged it for this generation, not the previous ones.