I will assume by "second biggest" you mean in land value, not acreage, where I don't think the Church is even in the running.
I don't know but I suspect most of the land the Church owns has a church or other religious buildings on it, and is "valuable" simply because it's centrally located in a city which has grown up around it.
A church building is only marginally useful for other purposes, so the get the full value from the land, you would have to tear down the churches and build office buildings or condos or something.
Would that really be in the best interests of the nation, the city in question, or even the poor?
“Some idea of the real estate and other forms of wealth controlled by the [Ed.: Roman] Catholic Church may be gathered by the remark of a member of the New York Catholic Conference, namely ‘that his church probably ranks second only to the United States government in total annual purchase.’ Another statement, made by a nationally syndicated Catholic priest, perhaps is even more telling. ‘The Catholic Church’, he said, ‘must be the biggest corporation in the United States. We have a branch office in every neighborhood. Our assets and real estate holdings must exceed those of Standard Oil, A.T.&T., and U.S. Steel combined. And our roster of dues-paying members must be second only to the tax rolls of the United States government’.” – Avro Manhattan (“The Vatican Billions”)