There's still lots of creatures around today that haven't changed much in multiple-millions of years - dragonflies, cockroaches, crabs .... they're commonly referred to as "living fossils".
"Arnaz called Mark's attention to the creature. To most folks, the fish might have been little more than a curiosity, but Mark was a marine biologist with a recent PhD from the University of California at Berkeley, resulting from his study of mantis shrimps in Indonesia. He recognized it immediately as a coelacanth, a "living fossil" whose body plan hadn't changed appreciably in hundreds of millions of years." (emphasis mine)
First off let me apologize, the spelling of the fish's name is "coelacanth."
Secondly, your point (and the point of several others) appears to be valid. Some species appear to evolve and others not. This is really a generalization of my original argument. I have not seen a satisfactory explanation for this observation. Unless perhaps evolution is extremely rare. In which case it would seem unlikely to provide a satisfactory explanation for the great diversity of life we observe.
[living fossils]
My favorite is the dawn redwood. Beautiful tree, there are some here in DC in the National Arboretum. They were known from Cretacious fossils, a grove was found in China in the late '40s.
I believe gingkos (the only species in a whole phylum!) is considered one also.