Certain factions, such as KH, that were not historically ruled by one very powerful family will hardly see the amount of generals increasing through getting babies: EB has limitted this to such an extend that it is nearly impossible. This triggers another aspect of RTW: adoptions & men of the hour. (The engine uses a certain FM's/territories ratio as a measure to 'decide' when a new guy joins the campaign.) So if you want to have more generals, you just need to fight a couple of larger battles with your captains - and hope for the best.