It’s to connect phone numbers to identities. Getting a physical sim in China involves going in person to a store where they keep your passport and a mugshot (you hold a paper with your number on it) in a database.

There’s no free WiFi without requiring a phone number. It allows the government to connect internet users to real identities.

Apparently there aren't any eSIMs in China that include a phone number. I'm not sure why.

I think this is why Apple releases the latest iPhones with physical SIM trays in China while the latest iPhones in North America are eSIM only

A big reason is that an eSIM is virtual, which means anyone can easily get an eSIM that allows them to punch through the great firewall -- a defeat that the Chinese government would never allow to happen

I only know eSIM providers for data