End gateway portals do not respawn

The game doesn't seem to check how end portal gateways currently exist on the main island, only that 20 of them have ever been spawned). End portal gateways can be destroyed using various means (water dispensed into the portal block, commands, Creative mode) and killing the ender dragon will not create new ones to replace the ones that have been destroyed. On Survival multiplayer servers, trolls could exploit this vulnerability and destroy all of them. They should be able to respawn.