CA is centralized and suffers from all the drawbacks of being such, including but not limited to censorship, lack of privacy, and centralization itself.
I don’t understand how it can be even seen as an alternative to something like pgp
It's a PKI system, and by far the most widely used PKI system at that. Calling PGP "the most proven, and most supported PKI technology" is just simply not factual. You may not like it, but that is no reason to disregard understanding why it is so successful and something like PGP languishes with basically no usage in comparison.
(As a rough estimate, there's something like 10,000-100,000 PGP users.)
The size of the keyrings of global PGP servers is knowable. I don't have a link to the analysis from which I draw the numbers, but the summary is about 100k PGP keys. Take into account unusable keys and duplicates, and some number in the (probably high) tens of thousands is a reasonable estimate for PGP users.
In terms of anecdata, the only people I've known to have used PGP where the ones working on supporting it in the email client; I've seen more evidence of S/MIME email than PGP, and even that is extremely thin on the ground.
I don’t understand how it can be even seen as an alternative to something like pgp