Using a good camera for your video call is simply showing respect to the person/people you're talking with.
Even flagship smartphones don't have studio microphones with 48v phantom power, 32-bit float, pre-amp gain control, etc - that's something you'd have to invest in separately no matter what. But if you can get better video for free, why wouldn't you?
I completely disagree that good video is a sign of respect. I consider people wanting video on in the first place to be a sign of disrespect. It is rarely important for getting work done and I see it as a waste of resources.
I agree that video is often unnecessary for effective communication, and I too avoid it whenever it's not requested. But there are contexts in which it's great, like occasionally seeing the face of a loved one, who lives far away; or helping debug an issue with a physical object (PCB, server rack, appliance...) that you need to see to understand what's going on. Especially in the latter case, having better video quality is just objectively better, especially if you can get it essentially for free.
But the builtin camera on phones is a huge area of attention for them. They tend to be amazingly high quality to the point of being overkill as a webcam.