[crote]

Security.

A lot of hardware devices pretty much implicitly trust the device on the other side of the data connection, because historically anyone able to run software on a machine also has physical access to the device. This resulted in devices accepting firmware updates over Bluetooth, for example, because how else would you update the firmware?

And now with protocols like Web Bluetooth, the only thing standing between between the average user and a random website completely owning their physical hardware devices is a single "I agree" permission popup.