The amount of space is the amount of space. You can't create more, because it's literally constrained by the roof of the plane. It's already maxed out.

The only thing they could do to make sure there was "enough space" is to have less tightly packrd seats and carry less people, which again they aren't going to do for the obvious reason - profit.

Or - reduce the max carry on baggage dimensions, which I'm sure people would equally complain about. And would make them look worse against other airlines which "allow" bigger bags, despite there not being enough space to put them!