How come some organisms haven't changed in over 50million years?

I recently sat through a long dragged out creationalist youtube video that only expressed one point to disprove evolution. They pointed to a handful of animals and insects that haven't changed in over 50 million years. Some of which included the mosquito, the wasp, some fish, the alligator and the list goes on. Of course the never mentioned any organisms that have changed, but my question is why haven't these organisms changed in such a long period of time. Are we led to believe that they never encountered an environmental change or competition from other organisms that would lead to some sort of change.