I'm surprised it's banned there... how could Snapchat possibly be threatening to the Chinese government? Are selfy videos really danger to the party? Were the keyword filters not effective?
Managing the software used to run a cloud platform isn't the hardest part of running a cloud platform. It would be a significantly larger effort for Snap to run and manage their own physical infrastructure. It's a big reason why Google Cloud is a service that makes money.
1) Ephemeral messaging. They want to keep records of what people are saying.
2) Reputation for sexting. Pornography is a major target for censorship in China.