How did most of the famous servers die?

For this, I'll focus on mineplex.

There are quite a lot of different little things that contributed to mineplex's eventual downfall.

For one, bug fixing took weeks, if not months to patch. I remember one time in a game players enountered a gamebreaking bug, but took a couple of months to fix, compare this to some server like hypixel, where major gamebreaking bugs are almost instantly fixed. Another reason may be that server operations were not as transparent as they should have been. I understand that most large minecraft servers are for profit and dont show much transparency. Lastly, Mineplex lacks constant updates to old gamemodes and additions of new gamemodes. Players will get very bored of the same gamemode with no updates. One of the big factors of hypixel keeping a very large playerbase, is of the constant updates that the dev team pushes.