You're sitting in the chair, waiting for the dentist. He arrives, and as he's getting ready to peer into your mouth, he casually says, "Yep. I graduated in 1971. Haven't done a bit of upgrading since then." Whoa. You're gone. You can't get out his office fast enough.
Just as we expect that professions such as law and medicine remain on the cutting edge of knowledge and expertise, we expect the same from teachers. What we know now about when children should learn concepts and how they learn them is vastly different from even a decade or two ago.