The short answer, is that since the Republicans get blamed for government shutdowns, whether deserved or not, the GOP is afraid of such shutdowns.
The GOP is worried what the liberals and media will say about them.
What annoys me is the surveys saying “who would you blame for a government shutdown”? It’s a biased framing of the question. Surveys should say something like “who would you blame OR CREDIT with a government shutdown?”
Several years ago, there was a shut. I think it was during the Obama regime. The Republicans were winning the media war, but caved anyway. If Republicans just held on for a couple weeks until people realized the world didn’t end with the shutdown, they would win the media war. Truth is, they don’t want to win that war.