Republicans, Ideology, and Special Interests

The other day on Vox, there was an article about the fundamental difference between the Republican and Democratic parties:

"the Republican Party is dominated by ideologues who are committed to small-government principles, while Democrats represent a coalition of social groups seeking public policies that favor their particular interests."

I just don't see how that works very well. Is it small-government ideology that leads the GOP to favor agricultural subsidies? Or increased military spending? Or Medicare expansions? Those increase the size of government and coincidentally help politically important groups that vote for and fund the GOP.

Or what should we make of this:

Here's my suggestion for the GOP. Say you'll support a carbon tax if it's used to do an equal reduction in taxes on capital. Even if there were no global warming, a carbon tax would be ten times more efficient than taxing capital income. Of course the Dems would say no. And then the GOP could taunt the Dems as follows:
"So Al Gore has convinced you guys that climate change will produce a catastrophe, and yet you'd rather engage in class warfare than solving the problem, Thanks for clarifying your priorities."
If the GOP weren't so timid on climate change they'd split the Dems right down the middle

That makes sense from the perspective of their (claimed) ideology. So why don't they do it?

Both major parties seek public policies that favor their interest groups. That's why they are the major parties.