I've seen this happen on another forum I use to go to.
It was for a popular crime show on TV at the time, and given the HUGE popularity of the show when it was on there was a LOT of activity on there, almost on a daily basis.
In fact, it was the VERY FIRST forum I ever signed up to, way back in 2009!
But here's the thing-after about 5 seasons that show eventually came to end, and it was most definitely FINALE.
Done.Finished.Over.Forever.
What happened?
Within months of the end of that show nearly all activity on that forum almost completely DRIED-UP!
Towards the end the activity on that forum was reduced to a snails-crawl, because the members soon realized that without any new import into the franchise in any form there would be nothing new to talk about in the franchise.
Or, to put it another way, when one Season ended (and when it was announced that the next Season would be produced but before production had actually begun) activity slowed down tremendously, and at the time some members were asking why things were slowing down?
Then one member-I can't remember their name/ID-hit the nail on the head:
The reason why there was such (has they called it)
"a lull" between Seasons is because everyone on the forum was just sitting quietly and waiting for the 'Next Big Thing' to happen in the franchise, and what will be released (TV show/film/merchandise) next.
Looking at it, I think that's exactly what's happened here. Tron fans and forum members are sitting quietly (making the occasional comment) just waiting to see what's going to happen next.
And I'm sorry but I think it's going to be a LONG time before we hear anything meaningful about this franchise. Tron 3 seems to have been indefinitely shelved by the looks of it, Disney have (so far) shown particularly no interest in reviving
Uprising and I can see almost no new major merchandising releases recently.
I'm sorry to say this, but by the looks of I think this is has good as it gets for the franchise for now. Legacy was released 7 years ago now, Uprising 5 years ago and I think that in terms of interest in the general public the franchise is very much on a declining slope now, and has been for years.
I don't think this franchise will disappear entirely from the Sci-fi community, it will always be around in one form or another and I think it's up to us to keep it going for as long as possible on forums like this.