None of them got very far. None of them actually was Ronald Reagan. None of them brought all the qualities he did into the ring. Some of them had voting records in Congress that made it hard for them to play the Reagan part convincingly (as President Reagan might have had if he'd been a senator, rather than a governor before being elected president).
Another problem is that you don't see classic conservative vs. moderate (or liberal) races in the Republican primaries any more. There will be one candidate who appeals to religious conservatives (Robertson, Huckabee), one supply-side, tax-cutting economic conservative (Kemp, Forbes), maybe one fiscally conservative deficit hawk, maybe one neoconservative war hawk, maybe one "constitutionally conservative" libertarian (Paul), maybe an old fashioned populist (Buchanan). They all split the conservative vote.
And with all those players in the game it can be hard to sort them out. It's easy enough in retrospect to say, "Bob Dole lost. He must not have been conservative enough," or "Poppa Bush wasn't conservative enough. That must be why he lost," but that's with a lot of hindsight.
Money. Specifically, campaign money. That's always been the bite for what the professional GOP campaigners scornfully call "insurrectionist" campaigns.
It would have bitten Ronald Reagan, too, and forced him into obscurity if it hadn't been for a very wealthy "sugar daddy" who totally believed in Reagan's message and went to the wall for him. Without that backing, Reagan would have been just another John Anderson.