The point is not to come up with a simple rule that is going to give you the correct answer in every case but to come up with a simple rule that is going to give you the best outcome overall. You need to think about it in game theory terms:

For friends they are unlikely going to be randomly malicious while assuming malice for every mistake is quickly going to ruin your friendship. So Hanlon's razor makes sense.

Corporations on the other hand cannot be assumed to have morals or care about you. You are already fungible to them so assuming malice until proven otherwise is not going to make things worse for you. Meanwhile giving corporations the benefit of the doubt allows the truly malicious ones to take advantage of that who, unlike your friends, don't really have any other feedback loops that keep them honest.