People are bored to see what they've seen for the past two years or so.
It feels like creativity has been lacking and no new idea's (as in not a few idea's but like constantly updates with unique aspects) have really been popping up to Runescape Private Servers for a while.
The custom scene has become a tumor where everything is about donating as much as you can to become the best and the private servers that do not have a too big of a p2w aspect got boring over time due to the fact I stated above.
Also the custom private servers I see releasing nowadays is just standing in a room and clicking pickachus and waiting for you to do 50k damage and then click another one (there's 0% skill needed and it's litteraly not fun to play since all you do is
click and wait).
To me (and what I've heard from others) a private server is quick play, and if nothing drastically changes have been done in a server for a few years straight, then it might gets boring (same as Oldschool Runescape at the moment).
For example an economy reset on servers like Runewild, Roatpkz, Alora and other big servers could do alot. A fresh start, new gameplay.
A server (or second world of an exsisting server) that resets seasonal would be an option to try out aswell.
The big players in the scene could make this difference, but are too afraid of the possible consequences (which I fully understand).