I think you're confusing two types of traps.
The bear trap is, if you'll excuse me being deliberately confusing for a moment, not a Trap. It is a piece of equipment that happens to have 'trap' in the name. The rules for trapmaking are not intended for building bear traps any more than they're intended for building Bridgets.
Traps are not something you 'pick up and carry around'. Traps are a piece of the landscape - a part of the architecture, so to speak. Bear traps are not, in and of themselves, a trap. Bear traps are, however, something you can USE to make a trap.
For reference - a bear trap can be hanging on the wall, and it's not a threat to anyone. It's easily spotted, and there's nothing close at hand to funnel someone or something into stepping into that bear trap.
However, once it's used to make a TRAP - it's laid out underneath a thin sheet of fabric covered with dust and light gravel to conceal it from the eye and casual inspection, along with arranging the surrounding rubble so that not only does the rubble look like it fell naturally, but it also funnels the individual through the environment to direct them to step into the bear trap. It requires the fabric, the time spent carefully covering it, the time spent replacing the fabric after you accidentally ruined the first sheet, it requires muscle to shift that fallen pillar a little bit, and then time spent getting moss to grow over the place the pillar used to be so that it's not obvious the pillar was moved. Arranging fallen debris against the pillar so it doesn't stand out as having been recently added to its new spot. There are several bear traps, in several places, to catch multiple people.
And this is a TRAP. And some of it will be lost in the process of springing the trap - the sheets will be lost, the gravel and dust scattered... you'll need to spend time and materials recreating it, after it's been sprung.
This is where the discrepancy comes in. Because a bear trap is just a potential trap. It takes artistry and skill to turn it into an actual trap.