No one knows. If you are curious why the ship and equipement in the "prequel" looks much more futuritic than in the original movie...it may be that the Nostromo is older or just not as good equipped since it has got a different purpose, no need of shiny stuff. Fly to this planet, mine that sh*t, come back. Only get out of the ship, if you need to repair stuff and so on.
The ship in Prometheus may be an up to date science vessel that needs high tech stuff for deep space exploration.
They would need slim suits as well and as you see they've got several versions of vehicles to explore the surface.
We already had that discussion a thousand times...in fact you can explain it this way. Someone compared it with up to date science to regular mine workers - in our time. The real reason is that they want to attract audience...you've got to satisfy the mainstream viewer,that wants fancy stuff, as well. Imagine you would use older equip than in Alien. See Star Wars Episode 1-3...better visual effects, better technology (or at least it looks better).
And there may be time travel...
greetings
Panda
