Why is it that mud thrown at Labour rarely sticks (at least according to the polls), whereas the distinctly lower-quality mud thrown at the Conservatives seems to have super-glue-like properties?

If someone said that the Conservatives wanted to raise countil tax by 4.4%, their poll ratings would drop in an instant. Even more than they already have. But the government have been raising Council Tax for years, it’s clear it’ll happen again, and yet their ratings are on the up-and-up. The Lib Dems want to change the system altogether, and yet nobody seems to hear their shouts.