God clearly prompts me to donate, above and beyond my onerous tax burden, in two ways: through Scripture, and by His Holy Spirit. So, what you're really asking is: Why does God ask that of His children? Only His children know the answer from direct experience. We are to deny ourselves, pick up our cross daily, and follow Him. He demands nothing less than all of us, including our finances. And He promises eternal blessing in return.
There's an old (nonscriptural) question that applies to this couple: by looking at your life, is there enough evidence to convict you of being a believer? Their budget shows no such evidence. They're living only for this world, serving Money and not God. I'm praying for them that, having willingly if unwittingly revealed that about themselves, God is able ultimately to get through to one or both of them.
No, you are selfish because you are piously looking for others to give away theirs. What you need to do is mind your own business.