It is weird because the scorpion, of course, dies too. And the frog was just doing him a favor.

I think the moral is supposed to be: "Some people are just irredeemably awful to the point that they'll self destruct and take you down with them if you try to help them" which... I guess is true but pretty jaded for a children's story, haha. Although, old fashioned fables do tend to have that dark aspect.