As a child who was the only child not invited more than once, I’m fine with the “everyone must be invited” rule IF the invitations are being handed out at school, the Scout troop, the Sunday School class, etc. If the invitations are being mailed, they can invite as many or as few as they wish.
PSSST - nowadays, kids can just invite the fire or police department, and a TV station, and get more presents than they ever imagined. ETA: Here’s the thread I started about it a while back, when it seemed to be on the NATIONAL news almost every day.
I’m guessing there’s a lot more to the story regarding the wedding invitations. Does the OP have a link to the blog?