This gem also springs to mind

Look up "the great attractor".

The "big crunch" is the (probably incorrect) hypothesis that there's enough mass to pull the universe into a single black hole - where everything is eaten by black holes, even all the black holes (nothing to do with the great attractor). The big bang in reverse

They do, but space is very big, and gravity is relatively weak in comparison.

The strength of gravity drops off exponentially with distance. For a star to consume another star they need to be really close.

This is made even more difficult when you consider they're all moving through empty space really really fast.