It mostly just comes down to having kids, right? I am certain that if I were single and happy staying that way, I would be living in a van in Moab and doing the bare minimum amount of freelancing to keep myself fed.
I would personally be extremely content living a very spartan life. If there were a barracks type arrangement where I just get a small room with desk and bathroom, and all food preparation were handled for me for a reasonable fee, access to a gym, and solid internet I'd be all over it.
But the minute you enter a romantic relationship, that generally stops being an acceptable living situation.
Biological answer: women had to hold on to resources to care for their ofspring, so it's hardwired.
Politically incorrect answer: they are self entitled nutcases. If you think you are spending significantly more than what you think you can afford, dump your wife if she doesn't agree to downgrade on the lifestyle to save on expenses