As long as it takes to gauge interest. It's no secret a hypothetical home release of the Westwood and Blue Water dubs would be a niche product, so much so that it's always been a question about whether such a DVD set would sell enough copies to turn a profit. Manga UK clearly aren't willing to take the chance. Yes I know they don't create their own DVDs, but if they wanted to they could licence the dubs and outsource the authoring to Visual Data London like they did with DBS Broly. Funimation, likewise aren't willing to risk it, but what they have that Manga UK and Periscoop Film don't have, which could be used to their advantage is a streaming service, so they are in an ideal situation where they can test the waters without needing to author, press, package and distribute DVDs. They just don't take advantage of it, just like they don't take advantage of the Pioneer movies being in their possession, and from a business perspective that's unfortunate as they are cutting their gains. Granted it's not by a huge margin but it's by something as there are plenty of fan's that would check out their streaming service just to have a way of officially supporting these old dubs or double dip on DBZ movies 1-3 just to not have to look for a second hand copy of the Pioneer DVDs.
I'm of the opinion that piracy should be avoided wherever possible, but the reality is companies like AB Groups/Mediawan Thematics don't make it easy when they haven't made an effort to make their dubs legally available for a full 15 years.