Because they also have the office of the president.
Currently anyway.
If one party controls both houses of congress and the president and has a sympathetic Supreme Court majority they can do a lot more than if they only have one or 2 of those things.
UnderpantsWeevil@lemmy.world 14 hours ago
“We need a supermajority” was a response Democrats gave in 2009 and 2021.
Did Republicans pass legislation they supported between 2011 and 2017? Did they pass legislation they supported between 2023 and 2025?