The movie itself has never been a big moneymaker; as others noted, Umbrella practically had to give their edition away.
Also, because of the various cuts and rights-holders in different territories, the elements are probably a mess to sort out. Even if it could be done, it would almost certainly be hard to convince the business folks at even the boutique labels that it would be worth it.
I don't believe in curses, but the Highlander franchise seems to have had one put on it a long time ago. Aside from the first movie, no one seems to have much desire to dig through all the ins and outs of the various versions of the sequels.
The currently distributed version of #3 (at least in the US) is a careless mashup of the International Version's picture and the US Director's Cut audio, and when it goes to cable and/or streaming, it's usually missing the subtitles for the Japanese dialogue. With Endgame, it seems to be a crapshoot as to whether the theatrical or producer's cut goes out. As for The Source, I've never even seen that one, so I don't know.
I'd definitely buy an edition of Highlander 2 with all the different versions included, but the work needed to achieve that would likely be a tall order for any label, studio or indie.