I wish they did that level of remastering for B7. They did do that for DW, going by every frame to fix every issue, regardless if it was on tape or film.
I tried looking for the source of that quote - I wasn't able to find it.
VT does have frames, just created electronically and at far lower resolution, then stored on tape. Between 1978 and now, means to edit frames from tape sources became possible. The BBC was unable to do the amount of restoration that they were able to provide for Doctor Who (with a larger audience).
I found a video that explains some of the differences between film and video - he's an interesting presenter and half the people I'd shown this to didn't like his style. The other half did.
Understandable, about not changing effects.
Regarding "they were so white", the film had the ability to hold more color and shadow detail (contrast). Videotape's range for color and contrast is much lower. When transferring film to videotape, a lot of detail was lost - the brighter white areas are known as "blooming". Conversely, darker gray shades would become black, which is known as "crushing". In the 70s, they had a video camera recording the film footage, and if its light settings weren't set properly blooming would be far worse... Nowadays, if the film existed, they could scan it with a drum scanner and capture every last bit of color, contrast, and other information then remove scratches and stuff afterward. The cleaned print could then be spliced between the videotaped elements instead of the grainy, bloomed, scratched and nicked material.
Being "too old" is possible; when I had subscribed to them 25 years ago, I don't recall them showing the Buck Rogers serials from the 1940s, and all those shows you'd mentioned are 40~50 years old and more.
Or because the licensing costs are too high for the estimated amount of viewers that would watch. But a lot of subscribers did flee as they started dropping shows from their schedule, and that started even before the rename to "Syfy" - which led to a lot of sardonic quips from folks as a result...