The party didn't want him. No one at that party cared enough to make less of an effort to inform him that there was a party than it would take me to get a glass of water from the kitchen.
Sending snail mail is pretty easy too. If you were to switch to only communicating via snail mail, do you think your invites to social events would drop? The events probably didn't want you anyways, since they couldn't be bothered to just send you the snail mail via this simple internet service. They're not your real friends.