Maybe the length of the saber doesn’t scale linearly. Maybe there’s some extremely fast dropoff in effectiveness after a couple of feet.

And the power limitations of the phasers seem to me like they require some kind of capacitor to charge up and release in a burst. Plus maybe the tip of the phaser would overheat under sustained fire.

And sure, you could say “add more tips”, but we’ve tried that with gun barrels IRL for the same reason. They’re heavy & unwieldy so they only get used for mounted guns, like with the minigun.