They were complacent and it cost them. Scarlet wasn't designed for that type of work, but General Stone was far too late to react and too passive with keeping the potentially infected quarantined.
Part 3 dropped the ball in many ways and once Skip and his Mum went on a side quest, things went real left.
Then the Marines get murked out in two seconds, just seem they threw them in there for no reason. Real wasted potential IMHO...
Marines served no purpose in this film. Very lazy writing.
The first half was great, then it gets worse but forgivable, but soon as marine scene gets introduced...it becomes unforgivably bad. Completely random, that one remaining guy...they would have exploded in the gas station if that situation happened lol another lazy writing, then he provides that corny forced up comedy relief for a bit. I understand movies need some comedy once in a while, but not this bad.
The movie is less than two hours and already has some unnecessary scenes. Whatever they have in a sequel they should have just fit everything in less than 3 hours in one film and made it to movie theaters.