You mean why, in the old system the revolts were much stronger? Because they were all independent and have full 100% of their levy. I thinks this makes more sense than having a temporary title and not get 100% levies of your co- rebels. A lot of time you even see the revolt leader trying to revoke a county and then when the revolt ends the count or duke has become independent. Plus you can't do a lot when having a temporary title, like marriage or kill them in jail...
Moreoever each rebel vassal can drag their allies in, which make the faction war a serious matter in the past.