An old topic, I know, but I recently read a very interesting article (it's in german, sorry) about why so many tv shows of the 90's aren't released on Blu-ray or at least in an HD format.
As you might know, most of the tv shows from the 90's were shot on film, not on video. The original film negatives could be transfered to HD, that's possible and has happened already, for example THE X-FILES being released on Blu-ray, since the film negative has an HD resolution. But here is the thing: Even popular shows like all the STAR TREK shows from the 90's were shot on film, but were transfered to video afterwards, because it was easier to deal with in post-production. Of course nobody thought about HDTV in the 90's, yet alone UHD. The video format has just an SD resolution, no HD possible. So in order to release a show like STAR TREK VOYAGER on Blu-ray you would have to hunt down the original film negatives, if they still exist that is, restore them, clean them up and do it again for every single episode.
The next issue are the special effects. By the mid-90's most special effects were done with CGI. These effects were of course only produced and rendered in the 4:3 SD format, since this was the tv standard back then. When Paramount produced the Blu-ray set for STAR TREK THE NEXT GENERATION they re-created every special effect shown in the episodes, simply to get it to the HD format. A lot of effort and a lot of money were put in this project, but the sales were disappointing.
Robert Meyer Burnett also said that an HD remaster of STAR TREK VOYAGER would mean four years of work, with costs around 20 million dollars. So this won't happen anytime soon, especially after the disappointing sales of THE NEXT GENERATION.
The article also mentions BABYLON 5. The show was also shot on film in the 16:9 format, but the effects were also just produced for the 4:3 SD format. When they released the show in the 16:9 format, they couldn't re-create the effects, because the original effect datas got lost over the years. So they simply zoomed into the picture every time there was an effect shot, which resulted in blurred images.
Which leads us back to MillenniuM. The show was also shot on film, even in the 16:9 format, including season one. You can see some scenes from the first season in the 16:9 format in seasons 2 and 3. The reason why it isn't out on Blu-ray yet might simply be that no one at 20th Century Fox thinks that it's worth the effort to go back to all the original film negatives, restore them, re-create all the effect shots and setting up all the used fonts again. They did it with THE X-FILES, as you can clearly see that all the headlines and fonts in the credits look slightly different from the old versions. And the effects look smoother than they did in the old material. They put the effort into THE X-FILES, because it is still a popular show. But I'm not even sure that the sales of the Blu-ray set did perform that well either. So unfortunately there is a big chance that we will never see MillenniuM in HD.