Ever wondered why the Republican Party, which is supposedly very conservative, always seems to nominate moderates for president? Well, there is a reason for this, even though that same party generally nominates staunch conservatives for other elective offices, such mayors, state legislators, governors, U.S. Congressmen, and U.S. Senators. Republicans elected to those positions usually represent districts, cities, or states that are fairly conservative. However, a President of the United States must represent all Americans, and the majority of them are independents who are moderate in their political views. Therefore, it is difficult for someone who is either extremely conservative or extremely liberal to get elected president.
However, it is would still be possible for a very conservative GOP nominee to be elected president, provided the entire Republican Party was unified behind him or her. That would be the starting point, the bare minimum requirement for a very conservative GOP nominee to have any chance at all to get elected. But the problem is that the moderates in the party would not only withhold their support from such a candidate during the primary season, but might also refuse to support that candidate in the general election. At least this is the theory that many Republican primary and caucus voters seem to take into consideration, regardless of whether it's actually true or not. It's called the electability factor.
So, what the GOP primary voters usually end up doing is nominating the most conservative candidate that can get elected, and this typically winds up being someone who is only moderately conservative. They do this regardless of the fact that they might like a more conservative candidate better. They do not worry about the possibility that the more hardcore conservatives might abandon the nominee in the fall. They take those voters for granted. They figure that hardcore conservatives would be so fearful of a Democrat being elected (or re-elected) that they would vote for the GOP nominee no matter what, because any GOP candidate would be more desirable to them than a liberal Democrat.
In other words, they just assume that hardcore conservatives have nowhere else to go, therefore the GOP insiders put their focus on appeasing the moderates, who would have somewhere else to go. Until the very conservative voters, especially those who are more concerned about social issues, put their collective foot down and vow to withhold their support from moderate nominees, this trend will continue indefinitely. As long as certain groups of people allow themselves to be taken for granted, they will be. Right now, the GOP doesn't have to buy the very conservative cow because it's getting the milk for free. And things are going to remain that way until that cow says, "No more free milk."