All social medias multi-user blogs are. It's a behavioral thing. If a specific behavior always guaranties results, then it makes sense to only do it when you need results. But if that behavior only sometimes yields results, then the brain kicks in and goes, "Oh, I should do this frequently, so that I already have [results] if and when I need them." This is good tactics, evolutionary. The brain that persist and has [results] should generally be better suited for survival than the brain that gives up and has no [results]. On an individual level though...

...it's only good tactics situationally. When the behavior is [LOGGING ON] and the results are [GOOD POSTS], then it's more of a vicious trap than good tactics. Especially when your time almost certainly could be better spent doing anything other than sifting through posts. This doesn't just apply to websites. Gambling exploits this behavioral tendency as well. Most video games employ it, intentionally or unintentionally, to varying degrees.