An important detail here is that in Switzerland it's somewhat normal to simply never pay back your mortgage, so many people will keep around a bunch of debt because it doesn't make financial sense to eliminate it.
When you get a mortgage it's usually broken into two amounts: an amount that you have to pay back (~30% if I remember right) and an amount that you don't (the rest). You can simply pay back the first amount quickly then pay interest on the second amount indefinitely. Interest rates here are extremely low (even a 15-year fixed-rate mortgage can be had for <1%) so you can keep the low interest loan and put the money elsewhere (e.g. stocks if you like to live on the edge).
When you get a mortgage it's usually broken into two amounts: an amount that you have to pay back (~30% if I remember right) and an amount that you don't (the rest). You can simply pay back the first amount quickly then pay interest on the second amount indefinitely. Interest rates here are extremely low (even a 15-year fixed-rate mortgage can be had for <1%) so you can keep the low interest loan and put the money elsewhere (e.g. stocks if you like to live on the edge).