A couple of reasons. First of all, I kinda need the microphone for work whereas I don't need a webcam. I also live alone, so it's not like I am having that many private conversations at home. However, I do for example spend time naked at home, and I'd prefer that to not be visible to any cameras.

There is thankfully a physical cutoff switch for the microphone whenever the laptop lid is closed in case I need to have a private conversation and ensure that there's no employee-provided microphones nearby.