Because in online circles, the 'alt-right' has basically become synonymous with white nationalism, advocacy for an ethnostate and/or belief in a Jewish conspiracy.
As the other commenter mentioned, the alt-right is to some extent an advocacy for white supremacy and white nationalism. It comfortably falls into the spectrum of the identity politics, as well supporting authoritarian strategies (nationalist border and trade policies).
Ben Shapiro is mostly a classical liberal with personal conservative beliefs. Anti-authoritarian, focus on individual identities and universal policy.
