I don't totally understand the concept of having an everything app. Isn't the OS the "everything app"? Do people like the wechat experience because you have one login and don't have to go through an onboarding process in every mini-app?
For Chinese people, you could say that WeChat serves as an OS with a greater coverage. It could even be said that WeChat represents half of China's mobile Internet.
Only after acquiring a substantial user base did WeChat launch its "Mini Programs". This feature has further boosted the usage of WeChat. For instance, during the COVID-19 pandemic, certain types of apps forced people in remote areas to start using WeChat. However, the fundamental reason is that the usage rate of WeChat was already high.
This explains why, outside of China, WeChat's "Mini Programs" aren't particularly striking: in those regions, there simply aren't enough WeChat users.