Because when I'm using my camera I make sure not to do things like walk naked in front of it forgetting that there's a camera there? For other people the thing they don't do while on a video call might be having an affair, or using drugs, or...

Your argument seems similar to "why would you care about a microphone spying on you 24/7 if you're willing to sometimes have conversations that might be overheard?"

Yes obviously when you use your webcam you're aware that it's not impossible you're being spied on, and some people may choose to never have a webcam for that reason. For those of us who are happy to take that risk for video calls, we don't have to also accept that we can be spied on any time the laptop is open.