As far as I know, only Apple and Microsoft operate in China.

At least iCloud is run by a third party and not Apple (GCBD). Similar to how Blizzard does with their games and why World of Warcraft disappeared over night. Important distinction to make when it comes to privacy and security (there’s none) and how Apple washes their hands clean while keeping the Chinese government happy.

It is pretty much a requirement if you want to do business in mainland China.

Firefox also had a set of China-owned servers to sync data from Chinese users to.

(“Had” because I think they officially stopped the relationship with Mozilla China)

Meta doesn’t. Their products have never been available in China.

Probably because the Chinese market is already full of Chinese social media companies. How do they expect to compete if they enter? It's not 2004 anymore where starting a social media on Harvard campus was a big ticket.