DarkCrisis
Let her cook.
I was extrapolating from a proposed scenario, a wire trap that had been detected. If I were DMing a simple wire across the ground could be easily avoided by stepping over it, no check required. If there's no uncertainty there's no roll. There may be certain scenarios where it would be possible to set it off such as if they were running away.
Why it's there isn't really relevant. Some traps can be easily avoided once perceived and there is no roll. Others cannot be so easily avoided. Which category they fall in will be a DM judgment call.
As far as why have traps? Why have any challenges or obstacles?
Just had this happen last game. The rogue discovers a trapped step on a flight of stairs. “Can we just step over it?”
Yes you can. Easy and done.