Tech pays so much, people can afford to move on.
That's probably the biggest reason.
I kinda reassessed who is benefiting and the actual importance of a lot of the work you do. Even though it's all framed as 'mission driven' and 'Changing the world' a lot of it really is only important so some mega corp can make a couple extra points on their stock.
I've talked to a bunch of people in the industry that had similar realizations. I've heard things like 'it's not something I can do today, but in x years . . .'
I believe there were a lot of people who reassessed an have a different view and that is and will continue to change the trajectory of many tech careers over the coming decade.