Because...???
Not to sound too insensitive but this is a point of view I genuinely struggle with. So, 1000 years from Trek the Federation collapses and that makes all those stories meaningless? I mean, I know Trek is fantasy and people need the fantasy escapism type thing but is it really a place of "I can't enjoy other Trek because 1000 years later it will all collapse in on itself?"
Hey....pssst. I heard in another franchise, the Galactic Empire falls. Does that make the movies before that meaningless?