Most tech companies have four-year vesting periods. Lots of people at my current employer, which IPOed in 2020, are still vesting shares from pre-IPO stock grants. As a result, those people have a very strong financial incentive to stick around.

Stripe is a rarity in that it issues one-year equity grants, which would make it more susceptible to brain drain after an IPO compared to companies with longer vesting schedules.