Why are heavy flaps better than just a bigger wing? Flaps increase lift during landing and T/O. But when retracted, they do nothing. The space needed to stow the common fowler flaps can't be used for anything else - fuel or structure. Extended flaps are thin, making them need more material to maintain stiffness. Moreover, they transfer their loads through the wing, instead of directly to the fuselage.

So, why do we use flaps instead of just scaling the clean wing up?


Is it because of concerns over cockpit visibility during landing? Can't we use video cameras do display the bottom during high AoA?
Is it because the extra lift - and drag - is unwanted? We can simply increase the cruising altitude without changing the cruise speed.
Is it because (for fowlers) the chord reduction really is that beneficial?  The larger wing volume for fuel leaves more space in the fuselage for everything else. And since the span does not change, induced drag does not increase.
Is it because slotted airfoil, as in many modern flaps, are not good for cruise? Surely we can add slots to the airfoil, and add mechanisms to seal them for cruise.
When flaps are retracted they do nothing, which is the whole point. The byproduct of lift is drag, a larger wing will create more lift, but more drag as well. More drag equals a slower cruising speed, or bigger engines to power past the drag along with higher fuel consumption. Flaps let airplanes cruise faster by getting out of the way.