Because I don't think the traps could pull in anything John might lose control of without some form of assistance, even if it's resorting to ritual supplementation instead of extra science. Mostly I am thinking of the fact that the Four Horsemen of the Apocalypse got pulled into one of the traps in the cartoon, but the trap then had to be sealed with wax that was stamped with a seal that'd been held for umpty centuries at a monastery in Greece, 'cos otherwise the Horsemen would get out. My brain was trying to construct something similar.

*sigh*