Apparently most of the key development staff have now moved on to other offices and even companies, so even if they did greenlight a sequel, it wouldn't be made by the same people.
That's not necessarily true. Some of them might not return, however, the people who made alien: isolation were very passionate about it, and it shows in the game. If the greenlight was given, they might actually come back just to work in it. Gears of War 4 is a good example. Made by a completely new studio, but there's still a lot of ex-epic game members who used to work on the previous games, now working on the new game.