e.g. savings accounts with 1% interest in the EU which are government insured up to 100k. Plus mortgage debt tends to have fiscal benefits in most countries, too. That's a better idea than paying off a 0% mortgage. Especially past a certain point where there's plenty of equity in the home.
There's generally virtually no financial reason to pay off a 0% debt apart from some edge cases here and there. People do it for peace of mind, which is of course fine, but it only works because of financial illiteracy as it's not the most financially optimal decision to make. (even not the least risky).
Meanwhile, getting 1% return on a 30 year mortgage puts you in a much safer, financially cushier position, than having had 0% returns for that period in time. Would you rather have 40k saved + 10k interest saved up in savings saved up in a government-insured savings account when you lose your job, or would you rather have a 40k lower mortgage debt and slightly lower payments or a lower time-to-payoff? Particularly given that mortgage payments can be furloughed and negotiated in times of payment difficulty. The answer is very clear. Choosing 0% returns over 1% returns in this case is the riskier choice.
Loan is structured in 2 parts: Bankloan and mortgage.
Mortgage is at roughly 0% and has a fixed payment for the duration - I cannot pay it differently than the initial agreement.
The bankloan is at (I believe) 3%. I've roughly doubled my contributions to this loan, making it roughly equal to the amount I'm investing each month. I'm missing ~$10.000 on it now, so I think i'll just pay it down and have that out of the way.
Being ahead also means that I'll have a way easier time if I ever need to buy something big one month - I can just choose not to pay that loan and not invest this month and I'll have plenty of money to spend. It's nice having some free cash flow :)
My wife stays at home with our 2 year old daughter.
We own an apartment in Copenhagen that we bought some 5 years ago, though we're obviously still paying a mortgage on it (0% loans definitely made that easier!). We're paying it down aggressively, though still have quite a bit of cash left to invest.
From my experience it's about priorities. We rarely go out to dinner and don't own a car - hopefully never will. Rarely buy new clothes.
While it might not be the norm, it's not something that's completely unheard of.
One major factor though is probably student loans. When my wife and I left the university we both had savings of roughly $15.000. A year later, we bought the apartment. That would have been impossible if we had debt we needed to overcome first. If your friends moved here with significant debt, they're definitely playing catch-up compared to their peers.