MAYBE IT'S MINECRAFT.... I might be playing it more so I'm spending less time on tpt....
People's interests often shift. one week, they're playing TPT, the next, they're playing minecraft. That's why some users just become inactive permanently. That's also why we gain users to replace them.
Another reason why there could be less activity in winter and more in summer is because of the holidays. In winter, students in USA usually get two weeks of vacation, and of course because it's christmas people want to spend time with their families, not on the computer. In summer, students usually get 3 MONTHS of vacation from school. The first few weeks, they may not get too bored, but one can get really bored if they're not busy doing schoolwork.
A mixture of the fact that it is the heat of the school year (in America a lot of students are taking midterms, me being one of them), and an overall trend of people drifting away from daily usage of TPT.
the aging original user base can be a cause too.
I remember I used to be on all the time between 2011 and 2012... but not that much anymore.
(I also feel like there was a drop in usage, at least from my perspective, after the pacbrad era)
Therefore, It is also because of the maturation of people as they get older.
yes, thats entirely possible