Well it's a spectrum.
If someone's opening up about something truly traumatic or difficult, they get all my attention and respect.
But if I feel like they're being a cry-baby (e.g. being hurt by words rather than their meaning, complaining with a plank in their eye, complaining without making efforts, being dramatic over a small difficulty/fear/etc., not pushing their limits, etc.) I cannot but feel repulsed.
Edit: as for the why, I guess because as men I think we should always strive to improve, face the abyss, and overcome dragons on a frequent basis. If someone cannot overcome the tiniest of dragon eggs, they seem weak and not worth my time. It's the antithesis of someone I want to emulate or associate with.
I'm like you, totally stoic. But if one of my mates has problems or is obviously in a dark place and wants to talk, it doesn't bother me at all, even if it is a, from my perspective, petty reason - we're humans and not rational machines, after all.