Because users understand what “microphone access” entails. “Use WebRTC?” means nothing to the average user.
Mobile apps require location permissions to use Bluetooth right now, even though that's a hard to understand situation for average people.
If a feature can be used to track people, you have to flag it off or else you are just contributing to the tech Big Brother apparatus.
Fair point, but "cookies" didn't mean anything to the average user either, and "cookie consent" banners are the norm now.