McCain appeals to independents who are therefore not republicans and not conservatives.
Meanwhile, conservatives hate Hillary so much that, at least in polls. they can’t bring themselves to pick her, so he POLLS well with conservatives.
But in fact, if they stay home, he will lose. All this proves is that if you get the conservatives to stick, the more liberal a candidate is, the more they can beat the democrat in a poll.
Not true.
Giuliani does not do well in head-to-heads. Your liberal Mitt does horribly when matched against Democrats nationally or in state polls.
The fact is that McCain is relatively honest for a politician and he holds great appeal for independents, which makes him highly electable.
Romney is seen as a slimy used car salesman with his finger in the wind and his eyes on the polls, and thus is very strongly disliked by independents despite his stances favoring gun control and manmade global warming and universal health care. And thus Romney is highly UNELECTABLE. There's no way he can win with the middle hating him and the right (correctly) suspicious of him.