Lot’s of good answers here. We just completed a new co-Cathedral here in Houston, and when I went to it for the first time, what occurred to me was an answer to this question.
It’s because the poor deserve MORE than just money. They deserve HOPE. The church is a shining beacon of hope for us all, and a beautiful reminder of the love of God for each of us. His love is a treasure more valuable than any money on earth, and it’s given freely every day in those ‘expensive’ church buildings.