I think part of the issue, and one of the considerations on any change, is that "trap spells" just aren't very useful in a general sense in an exploration-based game. The enemies aren't coming to you, you're going to the enemies. That means the only time traps are relevant is when you set them up and then lead enemies back into them, which as many have suggested is a waste of time since you can just shoot them.
But it also means that in situations where enemies *are* coming to you, traps can be very useful and so they have to balanced with that in mind. If beartraps locked enemies in place for a moment, that might make them far too good when doing Battleground missions.
I think making traps work would require a few things. First, additional missions or enemies to make trap setting a worthwhile activity. Some kind of "hunter-killer" enemies like an assassin robot that tries to get behind you and follow you would make traps a worthwhile means of stopping them. Perhaps enemies that set traps (a mine-laying urban crawler?) would also be good, to give players the idea of what to do with them. For missions, maybe a tower-defense style mission where you lay out traps and enemies have a few routes they can take. Or an "Escape the Horde" mission where you have to reach the end of a long winding room while being chased by an endless swarm of baddies.
Second, I think traps would require some rebalance on costs. Beartraps are essentially free but limited, since they're items. Other "spells" in that category either have unreplicatable effects (platforms) or offer a better alternative (moon lamps are a lot brighter than most other lights, but fall like items). If there were trap spells, I'd imagine they'd work well as high damage, high mana spells. That makes them a good choice for high mana characters, who probably don't have as many damage boosts so traps become attractive compared to direct fire spells (cheap but lower damage). If bear traps stayed in the game, something like a slowing or locking effect might be good, since that's something spells don't currently do.
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