Seltic or Keltic Celtics?

This is what I don't get: why are the Boston Celtics pronounced "Seltics" and Celtic music is "Keltic"? It's the same concept: ancient people, Ireland, history. The Celts are pronounced "Kelts" and the Celtic language is also pronounced with a "k".

So is Boston dumb, or what? The team should be called the Boston Celtics, with the K sound. Maybe they should pass out a pronunciation guide at games, or re-educate the populice over there. I'm surprised Harvard or MIT or those other schools haven't tried to fix this problem.