I agree with this because it is what I am doing right now in addition to my fulltime job, which is really not enough, but I have seen a lot of people who have found that their side jobs are bringing in more money, and as a result, they have decided to quit their fulltime jobs and devote their time fulltime to their side jobs, a good example of this is running a business, which is why you have a full time job and a side job. I have a lot of friends who quit their jobs to devote their time and energy to their businesses, and they have become extremely successful as a result.
devoting time, effort and money to develop a business is a good thing, i've done that and now my business is quite smooth. but the problem is when we see people leaving their main job just to focus on unstable side jobs
(like bounty or other freelance). if the side job you are currently working on cannot guarantee your long-term income then don't leave your main job unless you are ready to build a business.
We don't know if what issues they been thru on why they decided to quit their stable jobs for a side job but I guess its because the side jobs that you mentioned above are more flexible. Now they don't need to woke up early and got home at night very exhausted but they can now work whatever or whenever they like.
There are some people that can enjoy their life this way and they can sacrifice stability but they can still save up and use the money from something like ex. a business so that once it becomes a success, they don't have to worry anymore for their future. I'm with you by the way, I prefer more stability over comfort.