P0420: Can cats really just go bad on there own?

Hey all, I have a 2004 V8 4runner limited 184k miles. Been dealing with a P0420 code for a few months now. I'm considering replacing the cats(need CARB compliant). Do CATS really go bad on there own? No ticking, no exhaust leak, mileage 15.8 mpg, runs and sounds fine. I can't think of anything else. Only thing I have replaced are coils but I don't have a misfire. I've done cataclean twice following instructions, I've ran car at high rpm(4k), maintenance mostly up to date. So I repeat can cats really just fail without an underlying cause? I think this is what's holding me back from replacing the cats.