There are lots of jobs that can't be done by machine. It should be cheaper to have robot labour, they don't need sleep or breaks and can do things with a high level of consistency.
If it wasn't beneficial to the system in some way, rich assholes would be funding robot replacements for all menial jobs, leaving only human supervision roles.
We should be moving to automation to free up more and more of our populous from labour, but we'd rather keep people working than support people who aren't.
I haven't figured out quite what I mean to say but please discuss below.