Bluetooth builds in some buffering to deal with contention on the airwaves and packet loss while keeping the audio stream going. That buffer is the lag you are

Bluetooth builds in some buffering to deal with contention on the airwaves and packet loss while keeping the audio stream going. That buffer is the lag you are hearing. It is quite substantial, and there is a natural tradeoff here - you can use more power to (theoretically) reduce buffer size by improving the SNR of the signal, but if you run out of buffer, you are going to drop samples. Even USB audio has some buffering to handle bus contention, but it is quite small in comparison.