To me, the kickoff isn't meant to be as strategical as a punt. The team kicking off just scored (unless it is the start of a half) and the purpose of the play is to get the ball to the other team and give their offense a chance to move up the field. I don't think the NFL really wants to have kickoffs regularly near the sideline...which is why they've put in the harsh penalty for OOB kicks, and also have this rule in place. I think the general idea that is being promoted is for most kickoffs to come down somewhere between the numbers instead of having them close to the sidelines.

The live ball forces the return team to make a play on the ball. You can't just take a chance on where it bounces like you would with a punt...hoping it goes out of bounds or into the endzone. Anything close to the sidelines basically has to be fielded by the returner, so this rule helps the returner make the catch without being forced to have to watch the sideline if it is close.