The problem is that people are lazy and unable to stay committed. Or they just aren't motivated enough, lack passion, or aren't smart enough to monetize it effectively to make it more than a hobby.
I work a full time job, write multiple comics, advertise (whenever I can), run a website, run two patreons (don't ask), and write for video games that are slowly being made, and still have time to waste on an image board and shitpost as an anon.
You need to be dedicated and know how to make business decisions. I know of one person who turned their portion of a /co/ project into an actual webcomic but I won't name it because they want to keep that a secret.
My brand is growing and I use my job to help keep it running as it does so. I do expect to make a living on this... eventually. But I am dedicated and passionate about all this to be patient. I want to quit my job so I can focus on this full time. If I was running a /co/ project, it'd still be going and would probably be carried on solely by me.
Sounds egotistical? Well that's why most projects fail, you need someone like that running the show. I've been around enough writers and artists to see them running around in circles or just spinning their wheels. I've dealt with flaky people all the time and I have kicked them to the curb because they don't have that drive.