The volume in liters may be comparable between a Model X and (say) the Audi A6, but most large objects one needs to transport (furniture etc.) tend to be relatively cubic in shape.
If there wasn't a need for having big boxy trunks, surely we would all have transitioned to the (undeniably cooler) fastback-esque shape of a Model X / Mercedes CLS / BMW GT-series long before electric cars became a thing.
I'm sure the reverse may be true for some SUVs, perhaps there's some large wardrobe box that firs in an SUV that won't fit in the estate.
But wow, estates are sooooooo convenient.
Model X has 88 cubic feet with the seats down (if you have the bench-seat option)
Its a very big car.