Chests and Pants Sockets

Why does set legs always or 99% of the time rolls with a perfect 3 and 2 slots by default and regular legs does not? Why the discrepancy?

I am not really sure why some non-set pants and chests don’t roll max sockets, but if you want to know which ones don’t, you can look in the game guide and it tells you what stats will always roll on an item.