Why didn't Stump 'stop the steal' instead of just slinking away like a coward?

It was a big game. He never believed it.

Well, darling, that would be because there was no "steal" to stop.

As was clear when, in the multitude of lawsuits, no evidence of any electoral fraud was ever presented. Judges can't rule in favor of the plaintiffs when the plaintiffs present no evidence.

Trump knew there was no fraud, no rigging.  He was simply dumb enough to think that he could somehow stage a coup -- and people like Giuliani encouraged that belief by lying to him -- and then he saw an opportunity to raise a lot of money by playing on his base members' gullibility and general lack of knowledge and sophistication.

He was a con man huckster and fraud before he became president, and he left office not having changed one iota.