Those were mainly from the southern parts weren't they ? That was a pretty agriculturally fertile region too - wonder if the ancient volcanoes had any connection to that...

Anyway, by what I've read of it by the EB period Roman cavalry was decent enough if nothing to write home about, and for partly financial partly political reasons they mostly preferred to "farm out" cavalry duty to the other Italics at their beck and call. Heavy cavalry in particular cost like the dickies after all, so why not get someone else foot the bill ?