I see you aren't familiar with modern state of Minecraft servers. Due to Minecraft being limited to a one core big servers actually aren't a single instance. They use proxy servers(such as BungeeCord and it's forks) which distributes load between several lobby servers and from there people join one of custom gamemodes(Skyblock, Bedwars, etc). This allows for tens of thousands of people to play simultaneously, but not in the single world, while SMP(Survival Multiplayer) servers can run couple of hundreds at most. These giant servers are heavily containerized and automatically scale under load, so spinning up and shutting down servers is a pretty normal thing. And there have been some attempts to make Minecraft to run a single world on multiple instances(MultiPaper and some private ones), so even for usual SMP server it can be a commonplace soon as player join and leave.
> And there have been some attempts to make Minecraft to run a single world on multiple instances(MultiPaper and some private ones)
First time I hear about MultiPaper, another idea I had which I din't know someone was already working on LOL. It's a pretty promising idea considering the current performance problems of the game. This could possibly allow thousands of players in the same server which would be AMAZING, almost a completely different game. Imagine if MultiPaper was compiled to native using GraalVM.