Firstly let's first affirm what causes blindess due to the sun ( or solar retinopathy) it is caused mainly by ultraviolet light. It is quite unusual to endure permanent eye damage  from unassisted viewing, damage from which is usually repaired in a year or less. with damage from  devices such as telescopes which  focus light from a larger area than usual and causing damage before even the pupil can react, more usual. Most cases are due to a dark adapted eye being suddenly  exposed to normal sunlight; as the pupil has opened to let more light in;  this then lets  much more light than is usual through when sunlight is resumed abrubtly, letting quantities of uv light not usually possible, to shine on the retina. This happens commonly during unprotected viewing of a solar eclipse. This is also why you should check a pair of sunglasses  to see if they have a uv filter as otherwise the adaption caused by the darkness of the shades  can in fact increase sun damage.

  This is relevant as a human has a cornea that filters most uv light  from going through meaning that, unless  the human looks at the sun for an extended amount of time, the pigments are not likely to be damaged therefore it is not neccessary for such pigments to be  uv resistant and there is little evolutionary pressure to evolve such pigments  as humans to not tend to puporsefully force themselves to stare at the sun unblinkingly. 

many diurnal insects on the other hand need to see in ultraviolet. therefore other pigments in their eyes other than the ultraviolet ones need to be ruggedized against uv, plus the uv pigments would absorb some of the ultraviolet lessening damage. this combined with the fact that  many insects have a short lifespan whick leaves less time for the  effects of damage to have time to build up