Watching my aunts split a bill

Last night a bunch of us went out to dinner. This means both my aunts plus my uncle; Mother, Brother and SIL, me, and some of my cousins. The place we chose was cheap and fun. And my aunts made sure to split the bill between them.

I've seen them do this before—come to think of it, this is normal pretty much whenever the family goes out together. If anything the odd part this time was that only my aunts were involved in the split, instead of all the adults (or all the heads of households).

But it puzzles me, just a bit. I know that one aunt is worth millions—by which I mean somewhere over ten million dollars. The other aunt might be worth less, but the house she shares with my uncle is pretty nice and I don't see her economizing on simple things whenever I stay with her. So one way or another they are comfortable. The dinner bill for ten or twelve people (all relatives) was maybe a couple hundred dollars total. Why go to the trouble of splitting it?

Of course the decision is out of my hands: I don't live in the same town, so I'm just a visitor; also, even though I'm over sixty years old, in this company I'm one of the kids because there is a full generation ahead of me (Mother and her siblings). But if I were part of the process, would I play along? Or would I just say, "This is silly; I'll pay it and have done"?

I would want to do the latter. I also know that if I did it too often, I'd start to feel like people were taking advantage of me. I don't know how to make sense of this. It's a puzzle.

Maybe now that I've made a note about it here, that will prompt me to think more about it and come to an answer.