Bat Length Question....?

Im 6'1"/6'2" 205 pounds. Currently using a 33 inch bat and i've read from several sources that i should be using a 34 inch bat. i've looked at major leaguers and they all mostly use 34" plus. I know im no major leaguer but if "bat speed" is the most important thing in hiting, why don't mlb'ers use 32 and 33 inch bats?