He can just commit when he's offered the ride.

He can in that example. There are others where he can't. For example, the guy picking him up might have other ways of figuring out if he'd pay, and not explain what's going on until the ride, when it's too late to commit.

Is it actually correct that causal decision theory is mainstream?

I don't know. Both of them are major enough to have Wikipedia articles. I've heard that philosophers are split on Newcomb's paradox, which would separate CDTers and EDTers.

In any case, both decision theories give the same answer for Parfit's hitchhiker.