Me, and a few other researchers, have noticed that the creepypasta tend to become more active during later months, namely right before school starts up.
First theory, you have less distractions and you're less busy so you tend to notice them more. The summer is over, you're done hanging out with your friends and family as much. For others, you may have just been on your phone all the time. But, school is starting up again. You start going to it, and studying, which everyone can agree is boring. That may lead to your mind jumping to anything else that is relatively interesting, namely the creepypasta and paranormal experiences. It's more interesting than 2+2 = x, and you aren't distracted by your peers or phone, so it explains it almost perfectly. The only thing that doesn't make sense is why they appear now instead of, say, spring, where the same scenarios prove true.
Another theory, it's just the cold. People are weaker and slower in the cold, and the nights grow longer. Or, perhaps they just like the cold better. The dark provides them with a place to hide and watch, and generally, there tends to be less people out and about. It's better for stalking, kidnapping, and killing.
The next theory, there's something attracting them. Maybe someone is summoning them all, especially because people summon them around or on halloween. Or, maybe they come on their own. People in the past used to believe that halloween, or all hallow's eve, was a time of ghosts and spirits. Most believe that the creepypasta are nonhuman entities, so that could be a reason why.
The last theory I have, is that they're preying on the anxiety of people around these times. School is scary, and maybe they enjoy your fear. Maybe your cousins are coming over for the holidays, or you just don't like the holidays in general. Either way, people are anxious around this time of year, and it's a popular belief that they feed off of fear. It wouldn't be too much of a stretch to assume that's why they pop out around this time.
Those are the main four theories I have about why the creepypasta tend to be more active around this time. For all I know, there could be another reason that I haven't thought of yet, or even a combination of these.
