It's one of the things we pretend not to notice. Back in 1979 the Nostromo was high-tech looking, now it would look like a retrotech museum. The Sulaco which was supposed to sport tech from half a century later had stuff that looked high-tech in 1986. Technology marches on, and zeerust would be distracting.
I read that the prequel takes place 50 years before Alien but that my have changed.
Here is how I look at it.
The
Nostromo was the equivalent of a tramp steamer. It was never indicated in the movie that it was a top of the line spacecraft. The suits as well as other tech was just what the "company" was willing to spend on these long range mining ships and their tugs.
The
Sulaco was a military ship and all we really saw was some limited military hardware. We never saw the bridge or any other tech other than what was needed for the mission. We also don't know where they fell in the military. They may have been a bunch of losers or weekend warrior reserves. In the US the reserves generally don't get the top of the line equipment. Again the terraforming base may also have been older equipment that was good enough for the task at hand and it was mentioned that the terraforming machine was fully automated so the "colony" may have been just a rag tag group of prospectors making due with what they could afford.
In the third move, (spit), took place on a backwater prison planet were the resident inmates live like some sort of monks that shunned civilization.
The forth movie only showed the Betty which was a smuggler ship run by basically criminals that were dealing with a possibility rouge military guy on a mostly abandoned old military station. The whole cloning angle and labs hinted at much more advanced tech.
Think about it like Firefly. The Serenity was an old ship and didn't really show the true advanced tech of the Alliance. The core planets had floating estates and other pretty advanced systems as seen when the doc used an Alliance facility to scan his sister.
OK. On to the new movie.
The tech looks more advanced because it is a well funded expedition using some state of the art tech. My son had a problem with the little ball sensor the guy threw into the cave/ship but was the really all that advanced because at the beginning of Aliens you see a similar sensor being used to scan the interior of the shuttle. Sure it's on an arm and bigger but again you were looking at a bunch of guys on salvage ship searching for space junk to sell and it's doubtful they had top of the line equipment.
So I can come up with a rational that at least satisfies me for the higher tech equipment. Even if it doesn't convince my son.