It's not complicated.
It must be because you didn't answer the question that you bolded.
This isn't a situation where a majority of the Republican caucus is screaming for McCarthy's head for the reasons you outlined. That is not what is happening.
What you have is a very small minority of House Republican members who are trying to leverage their place in the thin Republican majority to force decisions with which the rest of the conference does not agree. So the question is why the vast majority of the caucus that
doesn't agree with Gaetz, et al, would simply give up and suddenly support whomever Gaetz wanted for the speakership.
There has always been the contingent of fiscal conservatives who take the position that Republicans should simply refuse to pass any budget legislation that doesn't meet all of their demands. And when that doesn't happen and the government inevitably shuts down for lack of funds, those same "burn it all down" Republicans want to play that game of chicken right through the end.
But we always lose when we take that approach. Every. Single Time. Because eventually, enough moderate Republicans who do not want the government to shut down for an extended period of time will end up siding with Democrats to pass the necessary legislation. The only result of that is the massive disruption that comes from the government shutting down, and Republicans looking impotent.
The fact is that if we want to reduce the federal deficit, we must have control of the House, the Senate, and the Presidency, Just like we had during Trump's first two years in office. Obviously, he squandered that in terms of deficit reduction, which just means we have to put somebody different in there this time.
But trying to force substantial budget cuts when you only (very narrowly) control one house of Congress is futile.