Why do academics tend to be reluctant to ask for help from other academics?
I have never been fully immune from this kind of behavior, though I've suffered less from it than others, a fact that most likely helped me land two really nice jobs. Let me survey a few reasons why I think it happens.

Note: I'm talking of mathematics, where "robustness" is not a thing, and talking to someone does not "contaminate" your thinking (unless you are really careless).


Bob and Charlie are too proud. They don't want to be seen asking possibly stupid questions in writing.
Charlie feels that he doesn't know enough to even pose a good question, and Bob doesn't care enough. (Students generally tend to have trouble gauging their level, and I have occasionally blundered into conversations I wasn't prepared for by asking a too-advanced question.)
Bob and Charlie have seen their questions ignored too often. (My personal experience is that the usefulness of emailing an author about a paper they wrote declines sharply with the age of the paper. If the paper is 15+ years old, they most likely don't remember anything and have the same perspective as any other reader.)
Bob and Charlie don't want anyone to know they are reading the paper, as they are worried of creating expectations. (This sometimes does happen -- in that an author takes a question as a stronger sign of interest than it was intended. Though it does not appear to be a big deal, but more of an awkward moment.)
Bob and Charlie are worried Alice will view their question as a personal attack or at least as a threat. (In my career of reporting errors, this has happened 1-2 times out of somewhere near 50. But this sort of risk aversion isn't exactly out of character for much of academia...)