Part of intelligent game play is balancing risk and reward. They know that they’ll be isk positive on the killboard so they do it.
To avoid becoming a victim of this situation it’s a good idea to use blockade runners (fast and cloaky), or a tech 1 freighter with Reinforced Bulkheads II in all 3 low slots when in HiSec. I can’t stress this enough.
It takes a lot more to kill a freighter so equipped and if there aren’t enough people in their fleet they won’t bother. If you put expanded cargo holds you are going to be out a freighter sooner than later. Your equipment gets scanned so they’ll know what’s in your low slots.