Forgoing revenues, potential profits and taxes on selling/leasing the property(@ pre-2008 market highs); writing off loses of rental income; property depreciation; betting on rising real estate prices(all were still chanting "buy RE, it will only go up" pre-2008). Those are some some possibilities I can think of, but IANAL or CBRE agent, but when I asked one why the blighted corners owned by the biggest earners on Wall Street during the skyrocketing RE bubble were sitting vacant for years, the answer was there was no expectation to sell or lease. And it was not a tank problem, the tanks were removed as the boards went on the windows.
edit: rewording & added last point.