Well, there you go.
This is the realization I came to, somewhere back in late 2000 or early 2001. I voted for Alan Keyes in the primaries of 1996 and 2000, and was sure it was a grand conspiracy keeping him from winning. I still think the primary system needs retooling, but what kept Keyes from winning was political reality.
To get elected, a politician HAS to get a large chunk out of the center. The far right can't do it, and the far left can't do it - unless possibly one end or another is split with a strong third party candidate. The candidates we'd regard as "ideal" the middle sees as "extreme", and they won't vote for "extreme".
The major parties have to get enough out of the middle to win, or they can't do anything. They are going to be mostly moderate, with enough "bones" thrown to the "ends" of the curve to keep them happy and on board (hopefully). The Democrats will give tidbits to the far left, the GOP to the far right, and both of them will save most of the goodies for the middle, because that's where the voters are.
The problem for far-right Conservatives is, until they change the country, they don't have enough votes to get ANYTHING on their own. If Democrats win, the right wing will get NOTHING WHATSOEVER. If the GOP wins, they won't get everything they want, but they'll get a few things.
So there you have it.
The Democrats will give tidbits to the far left, the GOP to the far right, and both of them will save most of the goodies for the middle, because that's where the voters are.
It's not so much that is where the votes are, it's where new votes can be picked up. Left, swing and right leaning voters are fairly evenly divided, about 1/3 each. Ross Perot and Ralph Nadar have now made sure that principled voters know a principled vote means getting nada. Only the truly delusional are now left in that category, continuing to fight for their share of nothing.