1) They used other services (e.g. Evite) which had the same effect 2) Nobody uses those other services anymore (okay, I got one evite from the one friend who refused to use facebook...and then somebody created the event page on facebook and all the party planning promptly got hijacked and moved there)
So your choices are to use Facebook and get invited to parties, or be like that guy from ten years ago who refused to get an email address and was butthurt that nobody would pick up the phone to personally invite him to the party.