As for your first question: I'm pretty sure I read something about "Romans being able to recruit their factional units outside Italy after Marius reforms"....somewhere on this very forum.

As for the second one: Greeks were at the time involved in quite a few struggles: Sicilian Greeks fought against Epeiros & Carthage, Mainland Italian Greeks fought in the service of Epeiros against Rome, Greeks & Carthage, and on the Greek Mainland + Carthaginians relied on mercenary armies (a small Carthaginian population controlling a vast amount of territory + the need for loyal soldiers...), and therefore couldn't simply 'replace/retrain' units like the Romans could - a whole different type of warfare altogether...