I don't carpool* because I hate having to be ready by an exact time each day, can't be done earlier and certainly not later.

If I was using an on-call car service that I could ping 10 minutes before I'm ready to go each day, I can do that without triggering my concerns.

*Note however: I currently commute by bus since I moved to Seattle, and I make up for hating being ready by an exact time by instead choosing a bus route that has a bus every 15 minutes.