We try to cultivate a mentor culture. We have internal mentorship, college internships and organized internal cross-training. You can even do extended cross-training in other teams and try out new jobs (within certain limits). And the fact of the matter is we're terrible at it; should be more organized, easier to access, have more objective outcomes, with even more mentors. I bet an unfortunate fraction of our people don't even know we have formal programs. But very large numbers of folks here want it to work, and keep helping out, keep volunteering. I could pick up the phone right now and probably get a dozen or so greybeards from the mainframe group who would say "sure, I'll show a new kid the ropes".
But you're certainly not an anomaly...there's clearly more people who would say "screw 'em...I got mine" than consider helping someone down the ladder.
And also, I've noticed my desire to mentor has (slowly) gone down over time. I'm trying to avoid ageism and certainly not assume that seasoned COBOL devs are less eager to mentor than junior devs, and I hope I'm clear in that I'm projecting what is something of a personal limitation onto my future self.