A Youtuber who has a subscriber base of 200k who got there by doing something very specific like gaming, making animations or whatever, can suddenly make Vlogs about his life from time to time. That Vlog won't get as much views for sure, but it has a much better chance to rank high in search compared to a smaller youtuber doing the same thing.
It's actually how I was able to pivot from affirmation videos which was more narrow to book reviews. Then from book reviews I could start talking about whatever if I choose.