Why do you have to rebuy traps?

Precisely and this is why it's such a high priority for many players because without that functionality there's no reason to even use traps

 

That's why I don't use them.

 

It's why I always have a free builder

 

Same here. I always leave one free for walls/traps and impulse purchases. Or, if it's about bedtime and I know one's going to be freed up during my next play session, I'll put him to work, and let the newly-freed-up guy handle the traps and such.