Don't Forget About the Renters

The NY Times has this article today about renters in foreclosure. When a rental property is sold in foreclosure, tenants are often evicted (subject to certain timelines and notice requirements that might be imposed by state law). This article describes Fannie Mae's policy of continuing to rent to paying tenants until the property is sold. This makes sense, because it provides a stream of revenue for the bank and it also keeps the property occupied. Why don't other banks do this when they aren't required to by state law?