Why are the viruses that require an envelope more sensitive to the environment than those that are naked? This might just be a confusion of the concepts of nakedness, because as humans we are more vulnerable naked than if we have say a lay of protection on such as clothes.
Because that envelope is made up of fat (lipid) molecules that are very sensitive to environmental conditions. The envelope comes from the cell that the virus erupts out of, not from the virus. Naked virions do not have this lipid covering but are surrounded by proteins which are not as sensitive to the environment.
We actually don't need clothes; we used to have a coat of fur just like every other mammal.