I'm not sure that I agree that it is. You can be logged into both Uber and Lyft awaiting rides. Good luck trying to be employed at both McDonald's and Burger King awaiting compatible schedules. What makes gig work so different is that your "employer" can't demand you to work when you don't want to.

You're not going to get fired from Uber for being unable to cover a Friday night shift since you're at working at Lyft Friday night. Can't say the same about McDonald's and Burger King.