First of all being non-profit gives them a hell of a lot of flexibility in terms of how they work. They don't need to show growth to shareholders, so they aren't just taking in young developers, working then to their bones for a couple of years, then spitting them out.
And even if they are (for example) only paying $300k TC instead of $250k base + $250k stock at Meta, as you say, there are still going to be engineers who believe in the mission and want work more meaningful than just selling ad clicks.
First of all being non-profit gives them a hell of a lot of flexibility in terms of how they work. They don't need to show growth to shareholders, so they aren't just taking in young developers, working then to their bones for a couple of years, then spitting them out.
And even if they are (for example) only paying $300k TC instead of $250k base + $250k stock at Meta, as you say, there are still going to be engineers who believe in the mission and want work more meaningful than just selling ad clicks.