The goal of promoting these small SUVs instead of sedans is actually because they’re quite fuel efficient: being in the same category as much larger trucks, they pull up the average fuel economy and take the pressure off manufacturers to make their highly-profitable bigger SUVs more efficient.
8000 lbs is not totally crazy for a delivery vehicle. It probably weighs at least 2000-3000 lbs empty (with batteries).
Imagine a small business that tries to mail ten pound boxes. If they can fit ten by ten per layer in the van, once the pile of boxes is five layers tall, you’re basically at the van’s specs.