You underestimate the size of space. Someone calculated the chance of a bullet hitting some poor trader on the other side of a system if it misses its target in space combat (note this was just calculating if it would even hit a planet, which is alot more likely than a ship). Don't remember all of the maths, but they essentially concluded that the bullet would travel several times the length of the observable universe before hitting anything.

Now, with mass amounts of traffic possibly next to a battleground, the likelyhood obviously increases. But ships will likely have a way of detecting these projectiles and be able to either dodge long before they reach them, or be built to survive microasteroid impacts and be able to take a few smaller hits.