Because they are the ones that people want. Lots of leftover early rod bearings and odd sizes (standards) that nobody builds anymore, so the price is lower on those. The later 8BA insert type are more common also, so hence lower price as well.
they are full floating and not made so you have to find what you can get. give me a call if you need some sizes 818-248-2371
where is the best place to get a set of .08 over pistons, basically engine parts? not looking for high perfromance stuff.