When everybody is selling pretty well the exact same product, you have to build something different and then tell the customers forcefully and repeatedly that it's better. My opinion.
There are some advantages in terms of being able to service the transmission and finals, and some gains in efficiency in terms of the power flow being all in the same plane as the engine crankshaft. What you gain though, I think you lose in terms of added weight, more moving undercarriage parts, track stress and wear. I hear that any day now CAT will announce they have an undercarriage that will hold up well for use on the high drive system.