Not sure if the picture I painted originally was unclear but these kids are already living a very comfortable lifestyle by most standards. Most outsiders looking in would say they are all spoiled brats which is basically what I feel like you're trying to say more politely. But, this is just their norm, it's very much a part of their interpersonal connections and shared experiences which is exactly why we try to attend as many as we can. We try to engage in the community and support these kids as a group by celebrating their milestones and achievements; birthdays are one such example. What you fail to consider is these kids do not care about the material possessions at all. They've never had a shortage of that so they have no want for it. That is not special. I've never seen a kid even look at the presents during a party. They get loaded up and opened at home. I know my kid often doesn't open them for days or even weeks after the party. At this moment, he has a shelf full of toys he got as gifts half a year ago that are unwrapped but unopened. He's never even played with them. Some of them he already had and so he'll probably donate them at Christmas. However, the idea that they got to pick a theme and an venue that represents their personality/interests and share it with their friends during a day of fun is what they thrive on. Being the guest of honor at such an event has plenty of social-emotional benefits (https://pmc.ncbi.nlm.nih.gov/articles/PMC6130922/).

There's nothing lavish about these events unless you seem to think so. A $20/day trampoline park is not lavish. A 2 hour arcade card at D&B is not lavish. I don't know what your frame of reference is but this is what we do on a normal weekend if we have no plans too, just with a smaller group and withot birthday cake to eat.