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I think the reason is this. I assume.
Probably, YouTube simply displays the most popular videos on the main page, taking into account their recency. But in this case, the approach doesn't work. For example, a game community has 20 million people (that's how many are interested in the game). Of these, 18 million watched the new promo video (a must-see for fans).
1.05 billion people are interested in cats on the internet, for example. But they don't share specific videos with specific cats. They just watch cats, whatever they come across. Maybe even not too regularly (unlike fans of the game, who, at worst, will definitely watch the promo video three days after its release). As a result, on the main page, we see a promo from the game, and not cats, although the former is of little interest to anyone, and the latter would be watched by every second visitor to YouTube.
Solution: highlight the most popular themes, and then select the most popular videos from them. Should we patent it? ))