Because the popular channels in a programming tier support the less popular channels. If a la carte gets pushed on us with in a few years the number of channels to chose from will start to decline. Eventualy cable companies will only carry a few popular channels because it will not be worth it for them to carry less popular channels if no one is buying them.
A la carte = A la crappy
Umm, ever heard the expression "only the strong survive"?
Let some good 'ol competition decide which channels stay and which ones get the axe. That would after all be the capitalist thing to do. -- In relative terms life is shorter than the blink of an eye. Remember that each and every day because in the end it's not about what you've done but how you've lived.