1. It depends on what you mean by "much more." Romney has been running as a conservative. He's no Olympia Snowe, or Jon Huntsman for that matter.
2. Romney has been getting 40% of the vote thus far. That means 60% have been voting against him. Also, he's had the backing of the inevitability narrative, loads of money, the only serious campaign with real organization, and loads of endorsements. Every possible advantage. Prior to the buildup of the inevitability narrative, he was sitting at the high 20's.
3. In 2008, McCain benefitted from a front-loaded schedule and WTA. In the critical South Carolina primary, he got only 33% of the vote, but won all the delegates due to a conservative split. Similar splits helped him take states that should have gone easily to Huckabee, such as Missouri and Oklahoma.
In 2008, the GOP knew that their chances of hanging on were tough after eight years of Bush, so they were more willing to nominate someone with a reputation as a "maverick", or even a true moderate (Giuliani). That was less true in previous years and will be less so in future years.
4. In 2000, George Bush Jr. was the conservative alternative to McCain.
Critically, all of the Republican nominees have been the so-called candidates in waiting in the year prior to the election, even Reagan.
Huntsman is certainly not a moderate, and Snow really isn't one either. Romney certainly has a reputation for being more liberal than he is
The Republican formula during the modern primary system (1972- present has been)
1. Nominate the incumbent President
2. If there is no incumbent President, nominate the runner up from the last incumbent President
3. In a rare exception to the previous rule, if the year is 2000, nominate George W Bush
