Well said, SoundFreaq and Zalithian.
Using 4, or 6, or 8, or 12, or (n+1) speakers to fill the (roughly) 1cc "room" between earphone and eardrum is, IMHO, obvious overkill.
And just to be clear, Sensaphonics considers the dual-driver 2MAX as our flagship in the custom earphone category. (Our true flagship is the 3D Active Ambient.) The triple-driver 3MAX offers more bass headroom, but the 2MAX and 2X-S are designed for reference accuracy. This is an important distinction, as we design our products for use on stage (and in other high-noise environments), with a monitor engineer providing a custom mix/EQ for each musician. In that application, starting with the truth is the preferred approach for most audio engineers. That (along with hearing health) is our sonic design focus, and always has been.
The need to have a "latest/greatest" model and to differentiate one's product in the marketplace is palpably real for manufacturers. Adding more drivers and/or crossovers is an obvious way to accomplish that, which is justification enough for some. In addition, higher driver counts mean those models will bubble to the top when customers compare specs. Similarly, we see specifications in categories like isolation and frequency response that are clearly inaccurate marketing-driven. There is also no doubt in my mind that extra bass drivers are sometimes used to compensate for the sonic consequences of a poor fit or easily lost seal. Sadly, this encourages louder monitoring, which has obvious long-term hearing health implications. But I digress.
Does increased driver count translate to improved sound quality? IMKYSHO, definitely not. Can it? Sure, but that correlates better with other design choices and implementations vs. pure body count. And as others have noted, it's all subjective.