It all depends on the requirements.

The Innova D4D doesn't make a lot of power, but it's cheap to build and economical (as good as the Isuzu 4JA1 or better, actually). A more powerful motor would drive the price of the Innova up without adding anything that the buyers need.

SUV buyers expect power, which is why the Fortuner gets the more powerful 3.0.

HARI also offers models with different engine trims. The base Grand Starex has a weaker non-CRDI 2.5, whereas the top-of-the-line model gets a 170 hp 2.5 CRDI.