I think we need to break this problem down into 1) Toyota OEM caliper problems, and 2) rebuilt / remanufactured / aftermarket calipers. I've actually had very good luck with original equipment calipers, and most have gone well over 100,000 miles. And OEM calipers that I've rebuilt with OEM parts seem to last nearly as long. Aftermarket rebuilds seem to last nowhere near as long.

Why would this be true? I'd suggest several reasons. First, there's the rebuild / remanufacturing process and second there's the replaceable parts they use. Both are highly suspect - mostly because low price is the single most important factor here. Third, there's the cores they start with. Are they Toyota cores or aftermarket cores. (There is a difference.)

Just my 2 cents.