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I‘m *guessing” that Toyota didn’t want to change the ride quality/handling a whole lot, so only is lifting the vehicle 0.7” Maybe. Whatever. As you indicate, if we choose, we can later have the vehicle lifted a bit more.
Don't overlook the mileage hit in the context of fleet averages. If you modify a vehicle to be more capable on rough terrain at the expense of fuel mileage, it doesn't affect the federal stats; if they sell enough with that option package, it does.
Not that I have any particular insight into their thinking, but I've seen engineering decisions that clearly prioritized tenths of a MPG on other vehicles.