It's about choice, as far as I'm concerned. Debt makes you brittle, assets make you flexible. Additional money right now is of low value to me, especially if I calibrate my spending habits to taking 20% off the top and stashing it and don't develop as many expensive hobbies as someone of my income bracket typically does. But having money put away lets me keep living decently even if I can't work, or I can raid it if I lose my job, or I can use it to help buy a house or put my (hypothetical) kids through college, if stupidly overpriced college is still a thing in 20 years. Having that flexibility is one of the best insurance plans on the market, and it's one I get paid to carry. How could I say no?

Besides, government insurance is looking like a pretty terrible deal to 27 year old me, even if I do live in a rich country. Exactly how solvent do I expect it to be when I'm 65? And it's not like I can retire at 50 on a government pension that doesn't start until 65, but I can on my own dime.

(Also, speaking personally, I'm an investment advisor by trade. Being able to talk about investment decisions in the first person gives me direct business benefits)