There's a big difference in a lot of charities in the US - but so much in that country is fucked up moneywise.
Bear in mind that they're also a church first and charity second - their main mission is to evangelise about Christianity. A huge and expensive HQ would also seem to be an issue in a "what would Jesus do?" way as well.
*one caveat, is that a lot of charities are bequeathed properties in wills, often with covenants that say that can't be sold, rented etc. I know Cancer Research get a lot of bequests in wills (for obvious reasons), and in the past have had expensive properties that they would prefer to have had to keep, but it can be difficult to override such a covenant.
