I troll several reddit conspiracy subs, youtube channels, and various other boards where these people hang out. The closest thing to a legit answer I can give to you is they claim it's because you can choose to leave your phone at home, but you're not gonna leave your arm or leg behind.
To counter your other argument about compliance, this is only Part 1. Part 2 will add this same chip to other things like antibiotic snot shots for common colds, your daily insulin injections, I've even heard inside Epipens. Basically any drug that can be injected, from a saline IV drip to your wife's chemo therapy, "they" are eventually gonna get ya. The conspiracists know no bounds of ridiculousness.