There was nothing to stop the Republican party from unilaterally averting the shutdown, and there's nothing stopping them from unilaterally ending it. They have the majority in both houses as well as the presidency, so they can pass anything they like.

The only road bump in place is the Senate filibuster rule - but that's a rule that can be (and has been) tossed aside when inconvenient. Recall that Republicans removed the filibuster from judicial appointments when they wanted to ram through multiple Supreme Court justices and hundreds of lower court judges.

The underlying problem is that the current Republican party wants this shutdown because it reinforces their half-century-long message that government is broken and gives them cover to remove federal workers.

It also doesn't help that the House is remaining closed to delay seating an incoming Democrat representative from an Arizona special election.

Expect this shutdown to continue for a while.