I'm not talking about people who are busy/ill and can't come - there seems to be parents in DC's class that for years have never brought their kid to a party or even bothered to RSVP and acknowledge the invitation.
AIBU to find it slightly selfish? I aim to go to all parties that DC is invited to - 1) for my DC to enjoy it and 2) to celebrate with the birthday child and so they have as many people as possible! To repeatedly not even RSVP to say you're not going and just never show up seems rude to me?