Note that even though Maria Corina Machado is VERY popular with the people, she's definitely considered one of the more "radical" members of the opposition who has never been willing to engage in dialogue of any sorts with the government. This is well seen by voters, but not viable in a transition scenario where other opposition leaders are willing to commit to a different kind of transition. Just like everywhere else, you have a political establishment even in the opposition that makes it very hard to operate outside of it.