For the same reason we run, screaming into a freezing sea when there are heated pools and waterparks available. Why we go on long, wet, muddy walks to take in the view when we could just as easily go for a drive. Why people walk up Snowdon rather than take the train. Sometimes a little adversity and having to fend for yourself a bit is good for the soul
I don't do any of that stuff. All of it sounds like punishment. What's good for the soul (in terms of, what makes me feel happier rather than miserable and tearful) is hot bubble baths, massages, fluffy pillows...
If I can't afford a holiday somewhere more pleasant and comfy than my home, I stay at home. Why would I want to "get away from it all" when what i'd be getting away from is lovely?
specifically camping... i used to do festivals - but the last time (eight years ago? seven?) it fucking pissed down all weekend. what are you supposed to *do*...? sit inside a damp-aired, flimsy, fabric pouch, essentially on the floor, unable to touch the walls because it will become a wet, damp-aired flimsy, fabric pouch. for hours. occasionally putting on waterproof clothes and boots so you can trudge through wet grass and mud to use a manky, cold, shared loo. then returning to your damp fabric pouch, and trying to remove your wet coat and boots without getting soggy socks, or bringing wetness into the tent.
then, even in warm weather you have to dress in bulky clothes for bed (to fend off the 3am temerature drop, and enable a night time loo visit), and if you're lucky, be forced out of bed by a tent like a sauna by 9am. added to which my personal problems with sore back/shoulders/hips and knees due to the various demands of airbed sleeping and living at floor-level, and the whole thing is a trial.