Because the 'Rats are what they are - big-government, dependency-promoting parasites. They are as advertised.
The Republicans were supposed to be the counter to all that crap, and advertised themselves as such. Instead, once gaining power, they became what they pretended to oppose.
Why D.C. isn't surrounded by burning torches and pitchforks as a result is a mystery to me. We don't need two Big Stupid Government parties, yet that's what we've got.
Now the question is whether anything will change before the whole mess collapses. I'm inclined to doubt it. But I absolutely refuse to let Republican apologists get away with their lame excuses and obfuscations.