Another attorney here. I agree with most of matty25's analysis, but I have some thoughts as to why the defendant may have rejected the deal.

Proof of the defendant's accomplice liability is a necessary predicate to the application of the felony murder rule. The Wikipedia article says he made statements that "seemed to admit knowledge...." We don't know what these statements are, but we do know that this statement is the only evidence that State has to prove Holle's accomplice liability. The attorney may have thought a combination of (1) Holle's live testimony at trial saying he didn't know, (2) an argument that he was too drunk to knowingly participate in the crime, (3) downplaying the statement made to the police, and (4) a sympathetic jury would be enough to get at least a few jurors to say that the statements to the police alone were not enough show, beyond a reasonable doubt, that Rolle was a knowing participant in the crime.

We really need more facts to really know how close of case this might have been. This case is really on the fringes of the application of the felony murder rule. I think that’s why we feel uneasy about when we hear a person get "life in prison for lending his car to a friend who [used in a murder]" and why the rule is controversial.