It makes sense though. Or to put it another way, it seems odd to expect that there's always a global thumbnail optimum for a given YouTube video.

So to bring in the most views, put out different thumbnails to attract different viewers. Ideally YouTube would have support for this where you can just upload a dozen thumbnails or so, and YouTube figure out who needs to see which.

Eh, Veritasium is now majority owned by PE now (Electrify). This is why they’ve been introducing new hosts and Derek is doing more intros / voiceovers - the end goal removing reliance on the original channel owner.

So does he need to do it to remain profitable or does PE need to do it to pay for all their overhead / etc?

Ah interesting, didn't know that. The video is at least 4 years old, so suppose it depends on when Derek sold. Anecdotally, I think all the new hosts came after that thumbnail video, but I couldn't say how closely the changes you mention followed.

In general, it seems this is a thing that YouTubers feel they need to do to avoid being swallowed, but the extent to which MrBeast does it could well be extreme, and thereby worthy of suspicion.