WeChat's success can't be written off simply as being due to China's nonfree internet. They faced a lot of competition, plus hostility from entrenched interests. In particular, China's banks, and financial regulators, have long been unhappy about the popularity of its and Alibaba's payments platforms, which largely bypass the banking system. The government has always controlled the chat aspect of WeChat, yes, but they were initially blindsided by WeChat's success on the payments side, and by the time they figured out what was doing on it had become too widely adopted.

Moreover, there are examples from outside China showing that combining payments and comms is a very powerful idea, if you get it working. Like Kenya's M-Pesa payments platform, which came out of mobile phone accounts.

So why haven't Western chat apps managed to integrate payments? It's not clear, but my suspicion is the much stronger political and commercial power of the financial institutions in the West, i.e. banks and credit card companies. Look at what happened when Facebook tried to introduce a payments system--they got a tidal wave of bad press, some of it motivated by distrust of Facebook and crypto, yes, but also a lot of bad faith attacks orchestrated by financial stakeholders ("what if people use Libra to launder money?", as if Bitcoin doesn't already exist). Then regulators started to lean on Facebook, which got the message and dropped the idea.