why are so many team members leaving Optimism at the same time

A bunch of people probably just fully vested after joining in the 2021 growth period. 

Also, agree with @six looks like they did a great job on launching an open source stack. Unlikely superchain becomes a thing.

Eng @superstate. Chasing curiosity. People, nature, machines. Hakuna matata, "Its a problem-free philosophy.”

Also typically when these things happen it means that the company is about to make a meaningful direction change and these people are not onboard.