It's very hard to gather full teams (usually 10 persons) in a small communities. Public matchmaking gives an opportunity to start a game in a minute from clicking "play", regardless of how many people you have at hand right now.
Small communities still exist, it's just that vacant places are now filled with strangers.
lot of thing happened, 6th gen consoles started a new way of using online games (no keyboard, no third party chat/vocal, no group chat out of game, no private server), then the industry pivoted away from private server to have more control on their games, then the whole F2P economy then GaaS took any agency out of players hands.
