Well, lets look at the Sun. It is 1,392,000 km in diameter. The distance to the nearest star is over 4 light years away. That's 37,842,921,890,323.2 km. That means the distance to the nearest star is over 27,186,007 times as far as the Sun is across. So what we have are VERY VERY VERY small objects at HUGE distances from each other all moving around. On top of that, to have an actual collision would require the two stars to be approaching at very specific vectors, velocities, etc. The overwhelming majority of encounters between objects in space results in both objects simply passing by each other. Collisions do occur, but it is pretty rare.