I think there's a degree of affluence at which the question changes from "how much can I give while still attending to my needs?" to "how much can I give while maintaining my social position?" If you're just getting by and you give all you can, there's a good chance that the community you're nourishing will pay it back in kind. On the other hand, if you're rich and give away most of your money, you're not going to get that lifestyle back. And I think that's where a stingy mindset begins to set in.
I also think more affluent people are often socialized to expect that generosity will be taken advantage of, which leads them to favor formalized charities where their responsibility is clearly and legally defined and limited.
The more affluent depend on their social position to gain membership in their community in a way that some others do not. Taking a vow of poverty means you reject that, and you probably don't have a position in a web of mutual obligation to fall back on.
That's an interesting way to look at it. However as someone with few/weak social connections, I feel like the calculus has been the exact opposite for me, as I've transitioned from broke college student to well-paid tech employee. When my bank account was near zero, I jealously guarded it, not having any reason to believe that charity to strangers or even acquaintances would be repaid. Now that I have plenty of savings, I don't think twice about giving away money, because I have no particularly elevated social position to guard (nor am I desirous of obtaining such).
I think the tipping point may be when you first get a job that allows you to save a meaningful amount of money. for me, this changed the question from "how much can I give and still make rent?" to "how much can I give and still hit my savings goal?". "will I ever be able to retire?" leads to a very different mindset from "how early will I be able to retire?".
I also think more affluent people are often socialized to expect that generosity will be taken advantage of, which leads them to favor formalized charities where their responsibility is clearly and legally defined and limited.