There is no reason that Weyland would presume that terraforming + colonists are the best way of investigating an incredibly valuable spacecraft.
Aliens was written separate from any connection to Alien, and the studio had Cameron re-write it as a sequel. So the logic of it is thin.
The presentation in the films makes it appear that Ash has a standing order to recognize alien stuff that is more valuable than the crew or mission and act accordingly, and the Nostromo stumbles across the derelict. Then Ripley takes so long getting home that the colony is already in existence by the time she's debriefed. And maybe the derelict is missed due to the violent nature of the terraforming initiation.
All of which goes out the window if Weyland had already sent a mission decades earlier.
The Company knowing the location of the the derelict and its deadly cargo wouldn't sent have sent colonists in the first place but rather an exploration team and it's unlikely that they Company would commences any kind of costly terraforming operation there.