The protocol itself sucks. For example, do you want to listen to have game audio and have a mic active? This is basically the main use case for Bluetooth and what are your options? CVSD and mSBC, both of which have notoriously poor quality. If you were lucky and bought fancier hardware, you could marginally improve things with FastStream or AptX-LL, a couple of vendor-specific, non-standards compliant hacks that were finicky to use at best.

As of 2022, there isn't even a solution, only the hope that BT5 might be have standardized support for marginally acceptable quality, provided vendors actually implement it. Of course, you can't buy BT5 hardware today and vendors have entirely ignored large parts of the spec before, so that's not exactly a great selling point.

If one vendor gets the protocol implementation wrong, that's a shitty vendor. If every vendor gets the protocol implementation wrong, it's a shitty protocol. Part of what makes good protocol design is knowing how to design something that can actually be implemented well by real humans.