1st this is an old game.
2nd Its not spreaded to famous flash game portal. Lets count how high is the chances that you can find Plazmaburst 2. X-Gen, hackedgames, Y8 (Well Y8 is kinda famous), Silvergames, Agames, Coolbuddy and many more. Newgrounds could attract many players to the game with armorgames too but it leads to the third problem.
3rd Lag, Spamming, hackers, while toxic community applies to EVERY GAMING COMMUNITY and skill difference (Seriously though every player seeks weaker player to farm while weak players doesn’t stand any chance).
4th Some players play singleplayer and if you’re using multiplayer as a point well it won’t cover singleplayer but its still freakishly small.
Tldr: The game is not well known and it has problems in multiplayer.