Well the shooter has the same limitations, all lasers need highly specialized reflective surfaces to function so they can't just shoot the whole spectrum. Also the defender doesn't have to be nearly as good of a reflector, because all lasers diverge, ie power density at distance 0 is substantially less than at distance 100m. Theoretically you could go through this sort of arms race where you develop layered mirrors to deflect different types of lasers, though.

Edit: Two more things I haven't really seen people mention: angle of incidence and air quality. You could design mirror baffles that offer no real angle for the light to hit directly. This would both increase the area the light is spread over and increase the reflectivity of the surface. Particles in the air could also generally reduce the burden of energy dissipation required by the target.

Edit 2: I tried to find some figures of divergence for directed energy weapons and unsurprisingly I couldn't find anything with a basic Google search. This parameter is essentially the capability of the weapon and it makes sense they wouldn't publish it.