Bingo!

Since it is very common for boarding passes and IDs not matching EXACTLY (eg. boarding pass has LAST/FIRST, and ID has FIRST MIDDLE LAST), perhaps this is why TSA agents sometimes ask passengers to say their name?

Maybe by doing this the can make sure that you are the person listed on the boarding pass? Most people (with the exception of a few FTers who complain about the "say your name game") when asked to say their name would have a natural reflex to say their actual first and last name.