Here's why:

* Blue stars are massive: Blue stars are extremely hot and massive. They burn through their fuel much faster than smaller, cooler stars.

* Evolutionary paths: Massive stars don't become "dwarfs" in the same way smaller stars do. They evolve into red supergiants, then supernova, leaving behind either neutron stars or black holes.

* White dwarfs: The term "dwarf" in astronomy usually refers to white dwarfs. These are the dense remnants of smaller stars that have exhausted their fuel and shed their outer layers. White dwarfs are typically the size of the Earth, significantly smaller than the original star.

So, there's no blue dwarf star because blue stars are massive and don't become dwarf stars.