Preference for large drivers?

Darkmoebius...The line array is the only valid reason to use small drivers. As far as spatial effect is concerned, a line array produces a sound wavefront like a point source far away. The distance to the simulated point source can be varied by curving the line array.

I agree with Onhwy61 about total surface area. In fact, my current speakers have four 8" woofers per side and extend beyond 20 Hz with abundant SPL.

As always, it's more complicated than just size. The drivers have to be designed for bass. If you were to make an array of several midrange drivers they would still be limited, although the SPL within their range would be stunning. The impedance of a typical midrange cone rises at it's lowest limits and an array of them can reach up to 50 ohms @ 50 Hz, depending on how they're wired, etc....
It's possible to have an array of eight 7" drivers that extend no deeper than a single 7", although it'll probably play a lot louder with much less distortion and handle a lot more power.

Darkmoebius: No. It's difficult to explain but well executed line arrays do not have the point source effect due to dispersion patterns, even at nearfield. The concept of pinpoint imaging from a line source is counter-intuitive but entirely possible, actually probable.

Dr_joe
Has it all straight.. Facts are facts, bigger the more you can do no doubt..

However I will add the reason for slimmer, smaller cabinets is exactly that. Appeal mostly, and to be fair most small speakers are used because they will perform better in smaller rooms, and smaller enclosures, so if you want Multiple 10 inchers, or a 12 inch, or a 15 inch etc.. You need enclosures the size of most peoples Closets in a house to get optimal performance and make them do what they should be doing.

some subwoofers get past this these days with high excursion and tight cabinets with TONS of power to overcome the need of Huge enclosures, basically Overpower it and it will put out some good bass, or do it the right way and have speakers that take up a whole wall and are very efficient needing less power :-)