Because the content itself isn't big enough for celebrating a big milestone anniversary.
Either a brand new game, or a rerelease of the entire back catalog on current gen consoles is big enough for a landmark anniversary like this. The only time something significant was released on a milestone MK anniversary was MKDA.
The FF7 remake should be the benchmark of how to celebrate a milestone anniversary of a major game...not DLC for a game that is 2 years old.
I disagree.
Hypothetically speaking, if NRS were to recreate the remaining 5 MK1 stages from MK1 into MKX and 3 Klassic Fatalities for the remaining Original 7, that would seem like a huge announcement.
I think that it would be a big enough announcement.
If Boon / NRS posted on Twitter that they were doing something like that for the 25th Anniversary, I'm sure that lots of people would be happy with it.
While I agree that what you proposed would be an even bigger undertaking and a HUGE way to celebrate 25 years of MK (I'm not denying that), I don't understand how doing something like what I proposed wouldn't also be a BIG announcement.
Sure, not as big of an announcement as what you were stating, but still a BIG announcement for the 25th anniversary, imo.
MKDA releasing in November 2002 seems to be more of a happy coincidence.
Had the game been delayed in production, it could have also come out in 2003.
FF7 is a brand new game, though.
What you're asking for NRS to do is to start working on a game, and release it within 1 year, a feat which
(unless they've already started working on something for the 25th anniversary) isn't likely given that the majority of games these days take 2 years (minimum) to make.