This assumes that companies such as TikTok control their timeline up to the individual post, perfectly analyzed in order to extract your unique traits, and they have specifics ads lined up for you.
Where - in my view - their timeline is just a bunch of random submissions. TikTik is just trying to sell ads and will try anything to match your profile to one of their active ad compaigns so they can bill their client more.
I'm confused at what you're claiming here. Yes, the submissions are rather random, but TikTok definitely figures out what type of content you like and what advertisements are most effective.
Your feed is almost certainly personalized up to the individual post, but I think if we are making an analogy to human curation it's certainly not working the same way behind the scenes.
Think of it like an attacker (the app) would breach a cryptographic target (you and every other user of the app). The attacker starts to send random messages or try to mess around with signatures/tokens/APIs and listens for errors, timeouts, spam filters, possible side channels until it learns enough to figure out how to predict how the system will behave and maybe even to influence it.
Both in the analogy and with the timeline out does not matter if you mix a few random messages between a test and another as long as you comprehensively keep track of how the target behaves.
Every interaction is a data point, some data points are more useful than others but none is useless
