I agree with you a 100% Harley. But I also think the majority of people flying twins are adding bigger engines for two primary reasons:

1. you can run two higher thrust engines at lower RPM for better fuel economy and less engine wear.

2. If the engines are going to be used for something else later, bigger engines gives more flexibility.

This of course requires an airframe that can handle the weight. And, when detuned, its still AMA legal.