Every person in these movies is a blistering idiot. Like, the levels of stupid on every single person in these expeditions is insane.
The original Alien didn't require the entire cast to be complete morons, unfit to even operate as an adult in society, much less be mission-critical crew on a colonization mission.
If it hadn't been for the android in the original Alien, they would have observed reasonable quarantine procedures and there wouldn't really have been a problem.
That's one of the main reasons I think these movies are bad. The writers either did not care enough or were too incompetent to write intelligent, believable, relatable characters that I actually grow to care about.