Every few days if you notice the algo giving too many fast-food style videos, it's worth it to aggressively use this to unfollow all these topics. Miraculously, the next time you refresh your feed, all those old interesting topics you used to be into will come back.

Overall the algo is very very recency-influenced. You can watch videos from a niche interest for a year straight, but if you then spend a week watching nascar, you'll never see anything but nascar videos for months unless you say "not interested".

I imagine they have found that for the average user, having a longer history doesn't improve G's metrics.