Why can a newly discovered organism require the creation of a new genus or family?

A newly discovered organism may require the creation of a new genus or family when it is found to be significantly different from any previously described forms.1

The primary goal of biological classification is to place an organism into an existing group based on its resemblances to and differences from known organisms. When a new specimen is discovered, taxonomists compare its characteristics—such as anatomical, physiological, or behavioral traits—with those of known species.123

If the organism is a new species within a well-known group, it is simply added to the appropriate existing genus. However, if the organism is so distinct that it lacks close affinities to any known members of existing genera or families, taxonomists must establish new taxa to accurately reflect its unique position in the biological hierarchy. For example, when unusual deep-sea worms were discovered that did not resemble any other known animals, scientists created the new phylum Pogonophora to accommodate them. Ultimately, these decisions are based on a consensus among experts regarding the organism's natural relationships and evolutionary history.1