I think that in general, liberals are under-appreciative (scared, even) of markets, and conservatives are under-appreciative (scared, even) of regulation and government. The fact that a carbon tax system is both government regulation-based and a market-based probably contributes to its lack of traction.

Use the right tool for the job. In this case, a free market solution (i.e. carbon tax) would drive carbon offset prices down, optimizing the solution without centralized control. What if moving fully to electric vehicles is only the 10th most cost-effective way of reversing climate change? With laws like this one, we're committing to a potentially sub-optimal solution, which means we have to find more dollars than we otherwise would need to solve the problem.

Note that the carbon tax (which I assume would include offsetting programs as the sources of carbon credits or the sink for tax dollars) does have some significant regulatory requirements and challenges; if you sell me an offset, how do I actually know that those 10 tons of CO2 were actually captured from the atmosphere? I think you'd need pretty strong regulation for there to be a workable international market in carbon tax credits, for example.