There are a lot of places
around Detroit for people to live if they weren't comfortable in Detroit. There are some extremely nice suburbs that you can commute to/from in 30-45 minutes which is still somehow an acceptable commute time compared to most other large cities in the US. You also have to consider that you can live in a 3k sq/ft house with a nice yard for 200-300k. That's very appealing as a tech worker looking to get out of SV or other "hot" tech areas.
As for importing workers, I think you'd be surprised how many tech companies are in the city already, I've seen a lot of people who suggest that Detroit is a top 10 city in the US in terms of work, one example is here: https://www.forbes.com/sites/joelkotkin/2017/03/16/technolog...