How come the bank that is suing me is not the same bank that I have been making my mortgage payments to?

The good old days where a bank knew its customers by first name and kept their mortgages in house as portfolio loans are long gone. Mortgage loans are now flipped, bought, sold, and packaged into giant investment trusts with thousands of other mortgages that are sold on Wall Street. In fact one of the legal defenses often used to fight these foreclosure actions is that the bank that is purporting to foreclose doesn’t have proper legal standing or authority to do so.