I suspect that for Pence it's the desire to maintain all possible viability as a future Republican Presidential candidate, and he'll have even less viability than he has now (which is saying something) if the Trumpkins see him as a snitch.
Mike Pence has long been said to hold a sincere belief that God wants him to be President.
The sad, and stupid, thing is that God presented him the opportunity to be president on a friggin' silver platter, starting on January 7, 2021.
If he had rounded up enough Cabinet members to invoke the 25th Amendment, he might have been President for only two weeks, but he would go down in history (despite his countless flaws) as The Man Who Saved American Democracy.
(Not incidentally, it would also have sent a message to the right in this country that some things really are beyond the pale. And if those in power don't send signals like that, people conclude that things like the insurrection really aren't beyond the pale, because nobody, or only the little people, got punished for them.)
And, of course, if Mike Pence had become The Man Who Saved American Democracy, he'd be in a far better position to become President than the next-to-zero-chance position he's in now.