I've really been working lately on not judging others, so I read the question from that lens. I'm not sure what the point is of examining this, other than to judge others.
Also, friends of my parents have a lot of money. If I had to guess, I'd say that their NW is probably more than your $10m threshold. They have to adult children.
One of their sons is pretty significantly disabled. He lives (thanks in part to their money) in a community that is semi-independent living. I don't know the details, but I believe he has his own home but is provided with services, check-ins, and resources as needed. He can hold basic jobs (bagger at a grocery store, that sort of thing). They also live in a very HCOL area, but that is where they worked, and now it is where both of their children and their grandchildren live. I'm sure they could find similar services for their son (though perhaps not in a LCOL area as this seems pretty specialized and unlikely to be in smaller communities), but that would mean moving away from their other child and grandchildren. Is it excessive for them to want to leave enough money that he is taken care of for life and never becomes a financial burden on his sibling, and so that the sibling can use money to--to some extent--relieve himself of some of the responsibilites so he can care for his own family (spouse and 2 kids)?
Oh, and the husband in the family has come down with a devastating, debilitating disease. (Similar to ALS) His mody is slowly failing him. As it turns out, some of their many dollars are going to go toward caring for him: bringing in a daily nurse to get him in and out of the shower, to the bathroom, etc. Of course they didn't know this would happen and didn't specifically plan for it, but they did plan to be able to cover whatever might come up--more than most people do--because they wanted to be dead certain their son was cared for after they were gone.
So, is their $10m+ unreasonable? Are they "FAT pigs"? Not in my book.
You never know what someone's life looks like, especially at a quick glance. Rather than spending time deciding what is unreasonable for other people, spend it figuring out what is most reasonable for you. To my cousin who makes >$15k/year ad is pretty happy, I suspect most people here would have numbers that look pretty excessive to her.