Question

Why did the Supreme Court expand the incorporation of the Bill of Rights?

to ensure they always had the last word
to ensure equal treatment for all citizens
to ensure all naturalized people could be citizens
to ensure all legal cases came before the Court

Answer 1

Answer: to ensure equal treatment for all citizens.

Briefly: Incorporation (via the Fourteenth Amendment's Due Process and Equal Protection clauses) extended most protections in the Bill of Rights to apply to state governments, so states could not violate fundamental rights and citizens would receive equal constitutional protections.