First of all, the bound tag does not exist - it's aliased to bondage, so I assume you want to suggest they should be implicated to bondage instead.
Second, I don't think these bound_* tags have the same criteria as bondage does. Bondage means purposeful restrain of a person for sexual reasons, but there are posts such as post #1071388 or post #1420687, which aren't sexual and thus shouldn't get bondage, but they still count as bound_wrists.