Any client software can do this for the users who want it. There is no need for the service provider to track user watch history on the server by default.
I’m sure it might be useful if your primary business is something like, oh let’s say, delivering advertisements based on users preferences and behaviour.
At the end of the day the recommendation algo is why tiktok grew so fast and is so sticky, users want the companies to remember stuff, just not to use that memory against them (ya right)
