Sometimes being outside easy nuclear strike capabilities of the superpowers is a good on its own. Plus lot less annoying environmentalists and I imagine plentiful fissile material.
If literally every nuclear bomb ever made was detonated in a world war, the fallout from that would be a significantly smaller problem than the steady-state radiation is on Mars right now.
The fallout will eventually decay, but Mars will stay an irradiated hellscape forever.
With a couple fairly simple genetic modifications humans could thrive in place with high background radiation, in a place where nobody can throw nukes at you for doing simple genetic modifications.
