Because we live in a 2 party system with no opportunity for coalition government. You CAN join any number of right of center party's anytime you'd like, but they won't actually win elections. But that's your choice. If you most value political purity over ever having a chance to govern, then sure, join a 3rd party.
In our 2 party system the political party's are very big tents - filled with all sorts of competing interests. The candidate that makes it through the primary process has to appeal to a plurality/majority of a wide range of views.
Politics is as much about defeating the opposition as it is about advancing your own particular set of issues. Sometimes just stopping the left is victory enough. 3rd party's can't do that - in fact they act as a spoiler and often help ones political enemy.
Here is where I stand, sir. This country is beyond redemption; if what passes for Americans will elect a man like Obama, there is no hope for their future. So, I am not looking to win any elections since the electorate has lost any semblance of traditional beliefs.
I will take comfort in being among those with whom I share common, traditional American beliefs.
If it pleases you to settle for an occasional victory which means nothing in terms of the country’s direction, good. You should know that things will never be what once were. Some people are willing to settle for very little, and you are one of them.
P,S, I could not help but notice your sadness is having to live under a two-party system “with no opportunity for coalition government.” My goodness, I bet you would be happy in Canada or Europe, where there is coalition government and they all vie for being able to run the welfare state.