I'd guess this is because shooting twice could target 2 different units and they didn't want it to work that way? There have been some similar changes to other units that no longer have to stand still to gain bonuses (Dwarfs I'm looking at you, especially now they can be added to Greywater Fastness) so it looks to be a shift they've decided on for the new edition. Maybe it's thrown in to try and counter the removal of shooting out of combat?
Yeah, of course battleplans will go and ****** up the best laid plans! The one thing I do worry about for me is wanting to make the most use of the great companies rule but then being restricted to a handful of units because I've sunk points into 30/40 guard, 30 handgunners and another unit to stay together as a block.
I probably need to get out of that mentality and not worry about a couple of 10 man guard units being too weak to cap objectives or screen potential allies.
Also, the points reduction for Demigryphs could tempt me into maybe 2 units of 3 to roam around.