Why is everyone so amazed at 1200 half hour episodes?
Not long ago, and possibly still, many Soap Opera watchers, who had to work, would tape their soaps and come home to watch 1-3 hours a night of their soaps. 3 hours is 6 episodes. So, although it may take a year or two (or more) to work your way through it all, it no different than coming home each night and watching the Day Time programming you recorded.
Which may be true of shows made in the last 20 years. Dark Shadows aired 20 years before that luxury was available to the general public.
And name me one single - and I mean single, not franchise - series in which 1,200 episodes still exist, let alone are being released to DVD at the same time.
You can't because there aren't any.
No soap opera that aired before 1970 exists in complete form in any archive - not Coronation Street, not General Hospital. None of them. Dark Shadow is the only soap opera of that era to survive intact.
And even if it wasn't, you would never see a complete collection of Another World or Guiding Light episodes released. Not just for logistics reasons, but because there isn't that much interest. Not even Coronation Street warrants that treatment. The best you can ever hope for are "Best of's" which has occurred with a few shows.
Dark Shadows, however, not only spawned two remakes (the 1990s series and the upcoming movie), but a comic book (Gold Key's comic outlived the TV series by several years, plus there's been a few others), Big Finish is now doing licensed audio dramas with original cast members augmented by alumni of the Doctor Who audios, and there was a novel series. No other soap opera can claim to be as fully franchised as this thing.
So, yeah, it's pretty special and significant and outright amazing for 1,225 episodes of Dark Shadows to be made available. Even if you're not a fan it's something to respect.