Well, most of these communities started with one person having an idea for an event and made their own server, rather than getting approval/permission from one of the larger ones. Over time it grew to be a staple of the community and the rest is history.
Which is how I started mine. I wanted to see more Crystalline Conflict tournaments so I made a discord server that I could customize to better feed information to team leads/friends. Sure I could have latched onto PvPrimal or Revival or some other large server but personally, I like doing my own thing.