Because I don't think the PS5 is expecting to get a bluetooth signal from a USB port. The USB cable is irrelevant- I don't think you could connect to a bluetooth dongle you plugged directly into the PS5, either.
If someone has a bluetooth dongle that's compatible with a PS5(does that even exist?) they could test it, though, and we could know for sure. There's no reason the USB cable would mess with anything afaik.