So there are two possibilities:

- There is no reason to take them and this process will slowly fail over time as companies who adopt these policies slowly push away talent options.

- You are not the target audience of a take home assignment hiring process.

I think it's easy to believe the first since it affirms your world view. Speaking as somebody who has a deep pocket of job opportunities and has taken one of these take home assignments, sometimes those opportunities become stale or you're in a tough market or need a job immediately. A number of companies who have bad hiring practices are still fairly acceptable to work at, even if it's not ideal.

TLDR - to pay the bills.