it happens because bluetooth profile for audio+microphone uses different codecs and has less bandwidth, due to being used for realtime communication.
the bluetooth audio streaming profile enables more codecs, but only playback, and allows significantly higher latency that you wouldnt accept on a call
My personal bluetooth ear clips do something much worse than adding latency - if they're not currently playing something, and a sound is supposed to come through, they omit the beginning of the sound while they get ready to become active or whatever it is they're doing.
Just delaying the sound and playing all of it would be a big improvement.
(Though that would fail badly for watching videos. That's something that uses 'headphones' mode anyway - why is latency OK there? It isn't.
My ear clips do add some latency, a noticeable amount, when I'm watching a video with mpv, and I adjust that by altering the A/V sync setting. They don't do the same thing when I'm watching something on youtube. I'd like to know what's going on there.)
the bluetooth audio streaming profile enables more codecs, but only playback, and allows significantly higher latency that you wouldnt accept on a call