Because you just...won't...listen. Ha.
You ask why people choose a pop-up over hard sided and if it's a look thing, then receive pages of answers and examples of why people choose pop-ups over hard sided (none of which were for looks) and then make a conclusion ("So it's a looks thing") that is the opposite of all the input you received. Ha.
I disagree with your above opinion that "if you're really going offroad then a pop up canopy would be the solution for sleeping in your vehicle". As outlined in my response, we drive trails when on long out-of-state trips and in our local Montana mountains that hard sided will not fit in. And, we do not want to overland in a pop-up canopy or rooftop tent as we like the insulation (from weather, cold/heat, dust, etc.), furnace, plumbing, water tank, instant hot water, etc. in our OEV CAMP-X. It is the perfect solution for us since it will let us get down tight trails with rock overhangs and tree-branches that a hard sided will not yet still is a full enclosure with all the comforts that we want in our camper and light/robust enough to do rough trails (South Draw Road in Capitol Reef, White Rim Road in Canyonlands, and other medium rated trails/roads). We have no interest, these days, in canopy or roof top tents. A pop-up camper is what provides the amenities we want (compared to canopy and rooftop tents) yet is compact and light enough to get down all the trails we frequent (hard sides campers are not).
I respect that for your use, you might have a different opinion on what is best or satisfactory, but please realize that everyone has different wants and needs and so maybe this thread was doomed from the beginning. Or maybe I'm just not following why you seem to have a predetermined outcome/opinion that there is no valid use-case for a pop-up camper except looks.
Not a looks thing; it's a function thing.
Pop-ups will fit the places we go (tight trails, parking garages, home garage) where hard sided will not.
Canopy/rooftop tents don't provide the amenities we want (insulation, plumbing, water tank, furnace, instant hot water heater, etc.)