As described in e.g. Rambam hilchos Pisule Hamukdashin chapter 18, there are bunch of things that render a korban invalid, and someone who eats from it gets whipped. However, there are three types of invalid korban that someone who eats gets kares: a korban that was prepared with intent to eat it beyond the specified time, a korban when eaten beyond the specified time, and a korban eaten by someone tame. (Others, that don't incur kares, are a korban that's tame, a korban prepared with intent to eat it in the wrong place, and an animal with a physical blemish.)
Why do those invalidations, specifically, incur kares, when other invalidations don't? I'm seeking a taame-hamitzvos reason, not a how-do-we-know (what's-the-d'rasha) reason.