A lot has been written about the social and legal difficulties of running such a site (how much do you enjoy looking at child porn all day so you can ban the people posting it? How many mass-shooters would you like to have post their manifesto on your site?) But I think the real issue is just money. Even if you keep things pretty stripped down, as 4chan or the original reddit did, hosting still costs money. And if you ever catch on, it's going to cost a LOT of money. Where is that money going to come from? Your users? You don't have a commercial product people are willing to pay for. Advertisers? Not in a post ad-pocalypse era; they don't want to be anywhere near a free, anonymous platform. And keep in mind that eventually you'll have to pay for ddoss protection, a security and moderation team, and probably legal as well. So unless you're wealthy enough to just pay for the site out of pocket indefinitely, any reddit or image board clone is doomed to failure from the beginning. It has a ticking death clock that will expire when the owners finally realize they can no longer afford it.