It used to be that managers would take capable workers under their mentorship and prepare them to move into their old role, as their manager was helping them do the same. Everyone extended a hand down to pull someone up, because companies promoted internally and hired from within.

That's not the case anymore. Your manager won't mentor you not because they don't want to, but because they're also struggling to find footing and progression in a corporate world where nobody gives a shit about the folks beneath them, nor do they have any vested interest in long-term organizational health. It's not personal, it's just the system our predecessors put into practice so they could have an easier time keeping money and power for themselves.

If we want to care about the careers of others again, we have to build institutions where mentorship and training happen, as well as where good ideas are recognized and rewarded. That's something even the most "meritorious" of SV companies completely lack atm, and they're viewed as the companies to emulate by the rest of the investor class and industry. Until and unless other companies reject those fads in favor of strategies that grow and improve their orgs from within again, we're all kind of on our own.