In addition to the great points people have raised, there is a slew of 4chan clones that are at least as functional, which never took off, or started taking off

In addition to the great points people have raised, there is a slew of 4chan clones that are at least as functional, which never took off, or started taking off then died. There are several open source projects around people have run up over the years. It's also not necessarily the most "uncensored", several such clones were famously a lot more open in certain discussions despite being effectively dead. And finally it's not totally ephemeral these days, with several mirrors showing up. At some point, any social network continues operating due to its critical mass of users.