Because it's a freaking pain to connect them, obviously! In my experience they work well enough once you have, but consider the experience of "plugging them into a different device".

Barely any devices support being paired with more than one central. So you have to tediously disconnect with the first device in some shitty menu (e.g. on Android the UI is not at all clear), then maybe put it into pairing mode (again usually though some terrible UI because manufacturers think pairing is a rare operation) and then finally pair it on the other device.

Absolutely ridiculous. Oh and what's the Bluetooth equivalent of a headphone splitter? Auracast? It's taken decades to get that and basically nothing supports it.

I do use Bluetooth things and I think the sound quality and reliability can be very good (if you're lucky), but the connection process is miles worse than plugging in a wire.