Same as with public transport. You can’t have because it’s haram for some political position

PKI is a pretty old idea. People were trying to deploy it in the 90s. It turns out that managing the issuing and authentication of keys, as well as keeping them secure and if necessary revoking them, is such a huge headache that few organizations have managed to do it properly. It might be possible to do better now with TPMs in laptops and phones; essentially this is why Apple Pay is now slightly more trusted than plastic cards.

The ability to make an infinite number of them.

And that most people have no idea how to verify any ID, so they need a system that turns any given form of ID into a nice and simple "yes" or "no".

I'm not at all clear what kind of ID is going to be genuinely useful for video calls, given we should only be trusting existing contacts anyway? But those things are why "private key" isn't sufficient in isolation.