Probably because it means nothing.
I think there are individual *causes* (as opposed to principles) that Republicans currently tend to support, patriotism, lower taxes sometimes, military spending, free enterprise, etc. Just as those who term themselves "liberals" tend to support certain causes like "helping the little guy," programs for the "poor," etc. But in my mind neither "liberals" nor Republicans possess any actual underlying guiding principles, so IMO neither really stands for anything.
It explains why both constantly endorse totally contradictory policies. For instance "liberals" have no problem endorsing ideas as discriminatory as racial preferences, while Republicans (obviously) have no problem endorsing massive government spending in spite of their support for lower taxes.