James Cameron when he made Aliens, made Weyland Yutani much more grey than the original 'black/white' evil company as originally depicted in Alien.
Consider the evidence:
The Weyland-Yutani execs who interviewed Ripley and stood in for Weyland-Yutani at the ICC hearing in Aliens were genuinely surprised to hear her story; and when Ripley suggested sending a ship to LV-426 to check out her story; they were like:
"No need to -- we've had a colony there for the last 20 years, and they've reported nothing out of the unusual in all that time."
If Weyland-Yutani was truly evil all along; why would they require Ripley to show up and explain everything to them? They would have simply sent a second ship after the Nostromo disappeared to investigate the beacon.
Instead, they waited fifty-five years before setting up a colony on LV-426, and then waited a further 20 years before seeking out the crashed ship.
This sequence of events suggests to me that:
The Company Directive that sent the Nostromo to LV-426 was not authorized by Weyland-Yutani's board of directors or anything. It was being done independently by an executive who was sufficiently powerful enough to also have the regular Science Officer on the Nostromo replaced with Ash. Thus when the Nostromo disappeared, the exec got really nervous and destroyed all the logs and evidence of him sending the Nostromo to check out the place. He certainly wasn't going to be fired or even held liable for the loss of a M-class star freighter with all crew and cargo.
So the Nostromo was written off as a mystery of space.
75 years later, Ripley shows up and Burke is sufficiently intrigued by her story that he tries to make a play for the upper executive ranks using this information as a springboard. My “fan-head canon” is that Burke knew the original executive from Alien somehow (or was related to him); thus when he heard of Ripley's wild stories; he would have gone: “Hey, that reminds me of the stories old man Dick used to tell me...” and decided to make his move.
In one of the key moments of Aliens, Ripley confronts Burke with:
"I just checked the colony log, directive dated 6/12/79, signed Burke, Carter J. You sent them out there and you didn't even warn them! Why didn't you warn them, Burke?"
If Weyland-Yutani was truly evil and behind the whole thing, it wouldn't be signed "Burke, Carter J.", it would be signed by the head of the Bio-Weapons division and initaled with five other division heads; rather than a mid-grade executive.
I realize that there is also another counterfactual to my speculation – as noted by “Kugelblitz” on AR15.com (LINK):
“Or it was just an "off the books" kind of a deal. Nothing committed to paper, anywhere.
Weyland-Yutani find out about something on LV-426. They look at schedules and whatnot and find Nostomo will be the next ship heading near it, put Ash aboard with his orders and off it goes. Nothing is ever put on paper, although I suspect the Board of Directors and CEO level would have discussed it off the record. When the Nostromo is lost, it sucks, but as far as the company is concerned it's no big deal. Whatever memos existed in the bio-weapons division is strictly under lock and key and not indexed anywhere. As far as the official record is concerned, there never was an order to divert Nostromo.
In time, it is simply forgotten. Maybe those who knew about the original plan simply dismissed the loss of Nostromo as just one of those things, ships might get lost regularly in the Alien(s) universe. Or maybe the higher ups decide losing one freighter and refinery is expensive, but expendable. Lose another one in the same area and someone might ask questions, so they just quit looking at LV-426. Those people move on to other projects, retire, die, whatever, but the point is the whole project is forgotten and because it isn't indexed, at least not without being in the know or having super high level access, it fades out of memory in time.
Then someone puts a colony on LV-426.
Ripley shows up, tells her tale, and those who can dig in the files that don't technically exist. Weyland-Yutani decides to look into the xenomorphs and need to know if there was something there after all. They need someone to send a couple of colonists. They pick Burke. He's also expendable, but he's so small that he can send people without raising too much suspicion. If it pans out, great, the colony will likely be wiped out anyways by the xenos so there won't be any witnesses and wiping the records will be easy. If there's nothing there, big deal. They look, come back with a goose egg and everyone is going to forget the incident ever happened. Either way, if Burke has to put his neck out by signing his name on the order, he's told there's a huge promotion in it for him, stock, bonuses, a corner office, whatever.
The colony goes dark, Weyland-Yutani calls on the military to look into it. It is probably a law thing, or they have the manpower if the xenos go out of control or something. Maybe there is a sweetheart deal between the military and Weyland-Yutani's bioweapons division to procure and produce the xenos for the military to use. In any event, they bring Ripley as an "advisor" but in reality to dispose of her on the mission. Burke goes along because it is his project.
The only snag was when the initial attack in the reactor went sideways Burke's own survival was at stake. The nuclear blast would have been fine to erase any evidence, and the company would happily trade a colony for the xenos.”