The problem is that with 'renting' out your buildings, you're still cash-poor. You may have the assets to put against eg. a loan or a judgment but I'm pretty sure they don't want to lose the buildings in case one of these multi-million dollar lawsuits goes awry because a fire sale is going to bring up much less cash.
The other 'problem' is that they're a "not for profit" and although they could have a bunch of buildings, if it's outside their primary purpose, there's a slew of taxes and other bureaucracy to make sure you're not a "for-profit" they may be edging against the borders between not-for-profit and for-profit as it is.
In the end, if they were 'investing', they would indeed have kept the old buildings some way or somehow, but they need the cash now for whatever reason which is why they're moving and selling in a buyer's market.