It's because, to put it bluntly, there has been a steady decrease in quality over the franchise. As John O pointed out, the earlier movies had people being relatively careful. People seem to be dumber in the newer movies because sloppy writing filled with tropes along with less good acting are both cheaper to do.
The focus in the newer movies is on writing the "mythology" as it paves the way for a living franchise. With an increasingly healthy backstory, they can keep producing Alien franchise movies ad infinitum. However, more attention paid to this takes away from the basic storyline as it happens on screen. People tend to pay attention more to the overall abstract ideas and less to the details, so this works out...most of the time.
The real problem here is poor character development. Ripley is a timeless figure - great character onscreen, lends herself well to development as she started out "soft" and got "harder" as time went on. She shares a LOT of parallels with Sarah Connor. Also, unusually, she has a story arc and then dies. I don't think it was a good idea to bring her back in Resurrection.
In Prometheus, some of the characters mattered somewhat because they were tied in with the backstory (Weyland, Vickers) and others were somewhat developed (Shaw, Holloway). There were a few red shirts, like the idiots that got trapped in the caves.
Covenant sees almost no sympathetic characters. Everyone is pretty 2-dimensional - David, Walter and the Engineers are the most interesting of all. I don't remember anyone else - just by their cause of death. "Couple stabbed in the shower", "floating head", "blown up" is how I think of them. The captain doesn't even make it out of his hypersleep chamber. How are we supposed to feel bad about him?