The amount of force on a voice coil is related to the length (LENGTH! Not the total amount of copper) of wire in the voice coil gap, the strength of the fixed magnetic field in the gap, and the amount of current being pushed through the wire.
As everything else in this business, it's a tradeoff: more turns on the coil gets you a higher BL product, but it also gets you higher resistance, higher impedance, and in underhung motors, only gets you more field strength at the limits of excursion.
Larger wire decreases resistance, allowing more current to flow (and thus, stronger fields) but it also adds to the moving mass, and can limit the number of turns you can fit on the coil. Also, you can only reduce resistance so much before amplifiers become unstable. (Car amps are sometimes designed to handle loads of half an ohm--this is extreme. Most amps today are designed for 4 ohms minimum.)
A bigger magnet adds to field strength, but also adds to total driver weight (not mms) and cost.
The people designing drivers spend a lot of time choosing how many turns are right for the driver they're designing, and the "best" answer is different for every driver you could think to make.