And DS9 and TNG are the only two series that could have a big crossover eps, without straining credulity.
Credulity, sure. But getting the actors together to film this? Impossible. They couldn't even get Terry Farrell! How could they get more for a "big crossover episode"? Notice in every single crossover with any of the series, you basically get 1 actor and that's it (except for Enterprise's last episode. You got 2 and a voice over). The filming logistics don't work out for more.
Besides that, I don't mind the random stop. It's basically just another station they're stopping at, it might as well have been one of the big mushroom stations, it didn't matter. We got a little more bang for our buck, and instead of saying "neat!", we're greedy and saying "I deserve more"??