> I don't know about the percentage of affected stars in a typical galaxy collision but note that you don't need a collision for two stars to affect each other.

True, but the way in which they affect each other is that they try their best to collide.

From that perspective, it's kind of weird if collisions don't happen.

Is it? Think of a single star during a galactic collision. It wants to collide with every star in the other galaxy. It gets pulled this way and that, so, in sum, it decides to collide with the oncoming galaxy as a whole. Unfortunately, despite having billions or trillions of stars, that other galaxy is mostly empty space. The poor original star that we were tracking was unable to collide with any star at all.

Well, why do we keep attempting to collide with the Sun instead of striking out for the center of the Milky Way? Everything you just wrote applies just as much to the Earth as it does to a star heading through a foreign galaxy.