Traps are not placed manually via the ground target reticule (I don't think anything in LoV even uses that). When you use the 'special action button' with the trap minions selected, it gets dropped underneath their feet where they were standing. You then need to press the detonate trap button to detonate it.

But yeah I won't recommend playing LoV on a controller, it's fundamentally an RTS game and you really want a mouse and keyboard to get the most out of it.