Optics.
Perhaps it is the plan to make DJT speaker of the house. The optics would not be as good if 45 opposed McCarthy because he wanted to be speaker of the house.
Now Trump can get a nomination without that fight against McCarthy.
After all, McCarthy is the first failed speaker vote in 100 years. We all know Trump's world consists of Longshots.
I was taught the same, unfortunately by people who never actually read the Constitution. Speaker is not an Officer of the USA, and thus not eligible.