How do Protestants explain the incorruptibility of Catholic and Orthodox saints? As far as I know, there is a vast body of evidence of incorruptibility of some saints in Catholic and Orthodox Churches. Here is a picture of the incorruptible relic of St. Aleksandr Svirskij from Wikipedia :

 

Such cases have often been presented as a proof of the correctness of the Catholic and Orthodox Faiths - as opposed to the numerous Protestant faiths (as far as I know, there are no cases of incorruptibility in Protestantism). 

I wonder if any attempts have even been made in the main-stream Protestantism to explain this body of evidence or was it simply ignored?

If there were such attempts made, then what main points have been presented?
Though it's difficult to speak for Protestants as a whole, my experience with them is that they place no significance on incorruptibility, and as a rule, they are suspect of relics possessing special properties. Nobody will deny evidence that an undecomposed dead body is in an unusual state, but I doubt that many of them will claim that such a state is definitely an act of divine intervention because of the person whose body it is. It might be safe to say that Protestants are much less mystical than Roman Catholic and Orthodox groups.