I think it's differrent internet culture and demographics, what is a computer or smartphone? To average people it could just be that app, QQ or Wechat, using a smartphone is using Wechat. Computers appear in China relatively late, for young people, they'd rather have a smartohone than a computer.
And lastly, user experience, apps in the west need to mind the laws and media, but in China tech companies basically can do whatever they want, so it's always the race to the bottom coz that's where the winner will be. So you have Wechat filled to brim with hawkers/salesmen/marketers with unfettered false ads, its "self-media" platform feeding people the most eye-catching junk articles. User experience doesn't mean much when the popualation is so big they can just lock as many people on their apps as quick as possible, then the picky ones are forced to deal with it as it's a "superapp" - everybody is using it and they are not going to change.
So there you have it, the superapp experience: your boss and coworkers messaging you at night and weekends; the local police where you rent your room asking you to register ID and verify face on their Wechat applet; your acquaintances and parents sharing the latest self-media top story about stoping drinking coffee immediately coz Americans found it's carcinogenic.