I've slept in the back of quite a few estates, nice and long, lovely flat floor - would certainly be a struggle in most SUVs!
Lifting a heavy tent (or anything else) into the boot of a low estate is much easier than over the lip of an SUV which is raised up high for *reasons*.
Long loads in the back of an estate is much easier than wedging them into the passenger footwell.
SUVs certainly have their place, if you actually need the ground clearance and off-roading capability, but sadly the overwhelming majority of modern SUVs are just a jacked up hatchback.
Again I am not sure what your angle is here.
How many people sleep in their car?
I knew a couple of rally fans who would hire an estate and do what you suggested as they followed the rally for the extended weekend but they still used a "normal" car the rest of the year.
Lifting heavy things in is a double edged sword. I mentioned my TT, its far easier getting heavy things in than an SUV granted, but its more awkward when getting them out than my other halves SUVs used to be.
I would use hers by preference when buying heavy stuff from wickes as it was easier to get stuff out at the other end. I preferred doing the more awkward lift to get stuff in when it was easier to get access than getting it out which had worse access obviously.
Its horses for courses I guess.
Historically as I said estates were a niche market, low sales so they held their price well second hand.
Most people didn't want the ugly, heavier, slower, less fuel efficient cars

Then they switched to SUVs
I am sure some mainstream EV estates will come. But no matter how you cut it, its a niche market compared to saloons and hatches/SUVs*
*(I actually dislike the SUV term as well for these but thats what the mainstream have decided to call them)
And yep agree they are basically jacked up hatches, but then many people really like hatches due to the size/practicality