Actually, I think the algorithm is far more complicated than you think. It's not that people were previously watching van life videos. It's that simplifying lifestyles, minimalism, decluttering, sustainability... These things have really been trending upwards. And the algorithm has really evolved into this thing that can suggest videos that will keep you in whatever hole you're in.
So for instance, I went from cleaning videos, to decluttering videos, to minimalism videos, to sustainability videos, to finance videos, to van life videos.
And if I would watch a video where someone who was all about minimalism suddenly talked about how minimalism improved their finances, that would create a new hole for me to fall in where suddenly I'm getting quite a few finance videos recommended to me.
Yes, there are tons of people with more well-established channels than Jennelle Eliana, doing van life videos. But if you pay attention, you'll know why she blew up so fast. She is just really freaking fun. She has a huge personality that so many other van lifers lose in post.
And she's not the only person with an interesting personality who blew up. It's just that she was lucky enough to blow up when her content niche was trending. Had it not been trending she probably would have had Liza Koshy levels and speed of growth.