I really don't understand why people are so offended and so full of their inflated self importance that it has to be a full invite or nothing
Because it implies the bride and groom want attention, admiration and gifts from these people, but don’t like them enough to pay for their seat at the table. Or share the intimate parts of the wedding with them, like the actual ceremony. It’s an invitation to a party not a wedding.
Nothing to do with self importance of the guest and everything to do with the bride and groom wanting to be centre of attention IMO. More people to congratulate them, admire the dress, take photos, give gifts at no extra cost. They can cherry pick the real guests.
They don’t have to include you in the head count for the meal and champagne, may not even notice if you turn up or not. I’ve never known an evening do include food and alcohol unless it’s a pay bar!
Most weddings include travelling, paying for a hotel, finding a babysitter/nanny, time and effort with hair, make up and clothes, buying an expensive gift. Why would you want to do that if the bride and groom don’t value you enough to invite you to the ceremony and meal? It’s like being invited to a wedding that’s not a wedding.