Question

why is the current classification system continually undergoing change?

Answer 1

well, because some things don't fit in the set systems such as animalia, plantae, protista, and so on. Scientists have to alter the system so as to fit those strange beings into a kingdom, phylum, class, order, family, genus, and species to come up with a scientific name.

Answer 2

The names you mentioned no longer exist in the updated system. The biggest reason is that at any level above the species it is an artificial system used by humans to group things. Since our knowledge of things is constantly changing we have to constantly redo our system of classification.