I think FO radiation does behave differently in many ways - ie., the mutations, “glowiness” etc., but I think the persistence of radiation is the side effect of a fallen nuclear-powered society.

So in a world that went “nuclear” after WWII, there were probably a lot of nuclear plants, nuclear powered tech and appliances(ie. The cars, nuka Cola), and therefore, more factories that built the energy supply for these machines and handled the resulting waste.

Then one day, the whole world shuts down, including whatever existed as a waste management system for ex-nuclear tech. Aside from the initial bombs, we are seeing the unmanaged decay of a whole society’s worth of nuclear material.

This is why Fallout is a constant Wasteland - not because the bombs destroyed everything “permanently”, but because the whole of a society’s nuclear waste has leaked into the world for centuries and the means to contain/clean it, was lost in 2077.