I have been a software engineer for more than two decades.
I'm not claiming server population is the only problem but it seems to have more than a casual relationship with server performance over time.
We know that before persistence 100 players was ok and that servers could run for weeks. So what does persistence add? It lets players permanently change their environment so that it can grow with players. This is obviously a bigger strain on the server and the server seems to be struggling to index the changes and push it to the clients in a timely manner. More players means more permanent changes to the verse.
When a server spools up it runs fine for about a day sometimes and then it starts to degrade until they need to shut down an entire region.
When server performance is degraded ( ASOP slow store / retrieve function ) , can't equip or buy gear, can't eat or drink food and if you log in and out multiple times you will see that lower pop shards on that server run ok while full shards have similar behaviour.
Kinda ironic that you say none of us know anything yet you can immediately rule out my idea it should work both ways. Either we both know enough to be dangerous or we both don't have any clues by your own logic.
My theory is that severs can't process too many players for more than a day or two. As players perform persistent actions in the verse it seems saving / storing that persistence and then propagating it back to the clients takes up too many resources as time server >0
Probably some memory leaks server side or DB is not optimised. Potentially CIG need to keep less persistent history ( I.e. drink bottles on floor ) and they need to cleanse low value persistent data tmore frequently to free up resources.
Perhaps they need better ways to manage their data like classifying it into simar groups with similar attributes and easier to recall location variables.
Having 50 players max instead of 100 should in theory reduce the amount of "persistent" data that needs to be stored, indexed and communicated with each client that comes into contact with each item.