Here is my input on this matter:
While they snare and can give Caitlyn a free longer ranged headshot, they are very weak by themselves. When I play against a Caitlyn and I know there isn't anyone around me I will step on the traps to get rid of them. In a controlled environment, you can step on them with very little punishment. During a fight, stepping on them could result in taking serious (if not terminal) damage. Dodging them during said team fight can be tougher if you aren't paying attention, or if it means making it harder to flee.
They also only stand for about three minutes (it might be four or five, correct me if I'm wrong), and it has no AOE effect. This makes them significantly more tolerable than the infamous Teemo mushrooms that can kill the beefiest of tanks with ease. They are also never cloaked or camouflaged, and do not leave behind any DOT effect.
Granted, this is a basic ability, not an ultimate. Ultimates should be more powerful as that is their design. However, Teemo mushrooms can be shot for a reason: they alone could otherwise kill you even when you're healthy.
Other potential theory: if you are in bronze, traps work like charms. When I play Thresh and use my Q, the enemy sometimes dodges it. 95% if the time, however, my opponent thinks, "Ooooo, shiny. Must grab." Needless to say, certain traps work like I do (much more than my co-workers).
Helpful tip: If you're Nocturne, you can use your w and step on any trap, Caitlyn or Teemo. They lose the trap, you leave unharmed, and your attack speed increases for a few seconds. If youre feeling cocky, thank the player who placed said trap.