Teasing apart motivations is hard.

There's definitely the "egoboo"factor, a term from the early days of user-generated content that has sadly passed out of use

For many, they're definitely a way to increase professional recognition, promote a consulting business, improve customer engagement/awareness, etc. i.e. brand building/content marketing

For some, it's a hope that they are going to hit it big though this probably applies more to YouTube and Instagram. (And, if there is a bubble, this is probably the main reason.)

The fact that even just a few thousand dollars is worth putting a fair bit of effort into for many.

Or a complicated mix of all of the above.