I think that many of the YouTube presenters started as a bit of fun or because they thought that they had something important to say. They then fell into actually making a living at it. But in YT you don’t actually have to sell stuff as you get lots of ads pushed your way anyway. In any case, a Lot of people learn a lot from YT, I’ve learned a lot from it for my wood turning where many of the presenters are clearly skilled people.
Partly, yes - at least for US presenters. There was a time early on that google ads was paying people $10-$25 per thousand views, and most people didn't use browsers. Ads were less dense, but I think google was just spending the money it took to draw content makers (but never let the content makers know that).
So, if you made a video every other day and averaged 100k views, if $15 was the average figure per thousand views, you'd haul in $1500 every other day. If someone got upset, they could file a false complaint about your video and it may go down for a day or two, and I've heard from at least some folks that google could drag their feet a little certifying videos as eligible for adsense (until they did, the views went through with no revenue).
There was a dude who made stunt type videos who had probably about 50k views on average, but made a lot of videos and some hit bigger amounts. He showed his adsense checks - $20k some months.
Then, I don't know, 8 or 10 years ago, advertisers learned that google and facebook were counting ad views that weren't really views in their accounting of total clicks or views, and the content creators started begging for money because the CPS went to around $2-$4. I never had ads on, so I only remember what they were talking about. Long story short, advertisers were throwing money at web advertising without much audit early on and when they got upset, they stopped doing that and the follow up was that ads cost them less. Some of the content creators were signing with studios who promised promotion, etc, but were really just looking to get a share of the ad revenue. And ad blockers started to get more prevalent.
So, when you get someone like JKM (I rarely see his videos) or Wranglerstar or some of these other people who were never professional anything, the video creators groups started devising other ways to get revenue. Making videos and referring to amazon becomes more valuable than the ads, as the click through on amazon may be 3-4%. Suddenly, people like Wranglerstar are finding the most expensive things they can refer (like $300 chaps and expensive coats or work shirts) to try to drive their share of ad revenue, and advertisers started going directly to content creators offering multi-dimensional revenue for sponsored videos (and the FCC in the US wasn't doing its job cracking down on these videos - they're adverts and required to be declared - now you see things like "sponsored video" in the top corner of a video). The multi-dimensional revenue is often something like $5k for two videos, then a "coupon code" that refers back to the video maker to get an additional share, and a link with a token ID.
As the videos get bigger, the really pretty ones start hiring editors and studio help and that drives the need for more revenue, but also fits the goal of getting bigger and the thing goes around and around. One of the YT presenters created a YT studio group to "help" content creators and ended up selling the business to YT or google for $500MM. Ad revenue falls into the background as being needed, but it's easy to lose it due to copyright claims or audio (same thing) in the background or anyone making a claim (and that's probably rampant).
So, what does this mean? When the method to get views becomes very standardized and the algorithms see what generates views, and more importantly, uneducated views of topically interested folks, it's a perfect recipe to catch people in the beginner's trap (when someone is just getting into a hobby and they'll buy almost anything).