Look at Wizards of the Coast. They've only licensed 5E because that's their current property, despite literal truckloads of books existing from previous editions which at this point is just free money for them. Doesn't matter. Publishers have to focus on the now, not the past. We're fortunate that Mongoose bothered to license 1E at all, because it's obvious (and flatly stated by MBM) that they want the focus to be on 2E.