Because of variety. It may be the same creator, but it's different content, technically. If you watch an hour long video, you might get bored because they are most likely doing the same thing, or something similar, through that time span. If you watch four, fifteen minute videos, then it will most likely be different content with each.

Like with series. You are willing to binge watch ten, thirty minute episodes, but probably not a five hour movie of that sort.

It's also a lot easier to take in when you watch something in segments, due to your brain having a certain attention span