A poll conducted by GSMArena suggests that Android Auto is used by 50.1% of car owners, while only 17.4% use Apple CarPlay. No insight into the “I use my phone with a holder” camp is given, as they could be Android or iPhone users.
Other poll results are below:
Changing the UI elements isn’t the reason why Android exists. The purpose of a phone’s OS is to act like a phone. Both Android and iOS do this perfectly well. If they didn’t, nobody would use them. Everything else they can do is just a nice bonus.
Don’t get me wrong, I much prefer Android because of those features (plus I hate walled gardens), but I think your usage of the word “purpose” might be a bit of a stretch here.