I'll only say this, since I want to be nice about it.
1. If you think about it, every job is unstable. Any job in the world has the ability to lay you off due to an economic shift that occurs. If you build up enough of a following, you could start your own website with your own video hosting service, do tours, merchandise, etc. Relating to a low time actor.
2. Entertainment is a service. Have you ever seen a movie? Of course you have. You have to actually pay for movies as well, and actors get paid for making movies. YouTube entertainers are more low scale.
3. YouTube can also lead to other real life jobs rather than solely internet based. My friend had a Hookah channel back in the day, and he was hired by either Fumari or Starbuzz.
4. YouTube has a net worth of 34 billion dollars. That isn't far behind Pepsi, which is still in business. And Pepsi started back in 1905.
5. Not everyone who starts YouTube goes in to it looking to replace it with a real life job. You can do YouTube and have a job. I've watched videos on people with around 50k subscribers that do it.
6. YouTube isn't something that could possibly just quit completely. There is so much varying content for you to find on the website at all times, it never becomes boring or repetitive (if you know where to look.) And finally...
7. Why do you even care man? Let people live their lives. It's their life, not yours. People want to play games and share it with YouTube, get over it. Don't assume you know why everyone on the site with 470 million views a day does something.
Any facts you want to check on net worth of websites, look up worth of web on Google and type YouTube in.