It has to do with how each has a little lag so if both were enabled you would hear the old stadium echo issue. So to avoid this Windows and most things only allow one at a time.

That said you could split off your ANALOG AUDIO (usually some 3.5mm plug and jack connection with a splitter to run to your normal computer speakers. Later you write about LAPTOP SPEAKERS which are not the same.

You later write about an audio switcher but that SWITCHES where I get the feeling you want both on at the same time and no switching.

I'll look for other solutions later but the fix for now is to use the audio out from the PC to a Y connection then to speakers and a Bluetooth Audio Transmitter.

I can guarantee you that the stadium effect will be heard if you can hear PC speakers and the Bluetooth at the same time.