As a UMich grad, most of us left because of the low salaries. It’s appalling how little software engineers make in the state and how much companies complain about an inability to find talent.
Salary is one part of that, but unless you grew up in the area, most non-hub-city regions are a hard sell for young folk, and Detroit hasn't yet recovered enough to be "hip". People used to have for move specifically to find a job, but in tech there are so many jobs available currently that you kind of get your choice of destination if you're a capable engineer, especially with remote work available.