It makes you wonder if there's a retirement-encouraged culture for inactive partners.

Which is probably what you'd want in a high-performance firm, less everyone look at the absent top level extractors and it turn into a law firm.

Equity holders are probably forever, and the incentive problems are a hard thing to solve. But you won't be a founder or early joiner if you're not allowed to keep your equity anyway.

Fortunately it doesn't take that much to get top talent, because so many other companies underpay. Jane Street only has to pay out a small fraction of their PnL and doesn't even need to have a non-compete.

with a profit margin at 70%, they can afford very high pay.

And the equity holders would get diluted a bit when new employees are offered equity, but looking at the rate of profitability, each new employee more than earn their share in equity, even at the high end. Therefore, it is in fact, in the existing equity holder's interest to get diluted a bit to hire these employees, who would produce way more value (and thus increase the total value) compared to the loss in dilution!