RX7 and Supra owners have to deal with an inline configuration to plumb and place dual turbos, whereas with a V6 arrangement you have one on either side of the engine. This provides for simpler placement, better heat shielding and simplified plumbing. "Heat soak" isn't an issue either as any latent temperature is eliminated as soon as you're flowing a volume of air through the intercooler. With the smaller turbos we're looking for quick, consistent levels of boost less than 10 psi across all RPM ranges. There just isn't any need for larger units, it's overkill and over spending.
We're not following the canon of street racers or the like, but proven motorsports design and fabrication.