Sound pressure levels. All things considered, more driver surface area is going to get you more volume, especially more volume per watt.
More driver area also introduces a variety of directivity problems, beaming, comb filtering, etc. That can be used to a sort of advantage - like in the line arrays in
@DanielT 's post above - but it requires sophistication for a fairly limited application, well beyond 'just wire all the drivers together'. In PA applications, where you need to push SPL to large open areas, this sophistication goes to both the location of the arrays and the DSP for combining and power shading them, otherwise standing in the wrong place sounds like hot garbage.
There are valid reasons monkey coffins, 5-way speakers with drivers splayed all over the baffle, and other similar visual complexities have gone the way of the dodo. (And not just that they don't fit in with modern decor, which is also a common problem.) There are also reasons why stuff like the Tektons haven't been done widely or long before, and it's not that there's some new secret sauce that's just recently discovered.