Output quality is a reason. Even if you have headphone jack, it’s usually built as cheaply as possible. Granted, Bluetooth headsets can be OK these days.
Come to think of it, do Bluetooth headphones only use class D amplifiers? Seems like it’d be hard to fit any kind of decent class AB amp in there. Class D amps have improved a lot in recent years, but you still want to use an AB if you’re serious (not even audiophile nonsense, just somewhat serious).