First off most of the morphs dont cause them to die prior to reproduction, they're nocturnal and they hide most of the time so coloration really isnt going to be that likely to lead to death. They breed fairly well, have a wide geographic range, and are probably exposed to a decent level of background radiation.

Since there really arent many selective factors for or against the various morphs in the wild, any that do spring up will probably stick around. Thus there are a lot of morphs.