Do you know the reason why my factory only producing car floor leds in 5V USB?

Because 5V usb type much better than 12v and 24v car floor leds.

5V USB car floor leds are less heating happening, so they are much safer than 12v and 24v car floor leds.

I attach picture of our 5v usb car floor leds now and then you can check it by your free time.