I think they get it, it's just that standing inside a cramped room filled with Knights, which will soon spawn more Knights right behind you, is not a very effective way to continue living.Maybe, but I don't think they get that the enemy can actually capture the base.
If I was going to fix that round, I'd get rid of one, if not both Phaetons, not have enemies spawn inside the garage except crawlers and watchers (and maaaaaybe low-level soldiers) and have the majority of enemies spawn outside the base and charge inside. Knights are just too bullet spongey to have them endlessly respawn img right on top of you.