It’s a safety thing. Older 4runners were the reverse of this because they had very thin side walls and a boxy shape, so to maximize cargo space (and in the process decrease safety). All old SUVs are like this.

Now you have to fit in a crumple zone, and airbags, and noise insulation, and blind spot sensors, and additional wiring. You’ll never see a vehicle that matches the spatial efficiency of itself 20 years ago because we require too much crap to be shoved in the sidewalls.

Now we’re shoving in batteries, so it will only get worse.