If you want my cursory opinion a big problem is that there is an unnecessary and often unthinking conflation of classical liberal philosophy with classical liberal economics. For example, Bentham advocated full employment via monetary expansion, but also pioneered utility maximisation, and now hundreds of years later we have economics based on the latter that denies that the former could ever be necessary, as general equilibrium (absent any short term frictions) will always ensure that those who "voluntarily" offer their labour in exchange for payment can find work.
Wikipedia has a very nifty quote which says that mainstream economics is rooted to the "rationality-individualism-equilibrium nexus" whereas heterodox economics broadens to the "institutions-history-social structure nexus". For all its prominence, most economics in politics is very superficial. If you don't know where or how an idea originated then you can't accurately explain, critique, defend or apply it. This applies as much to a Green saying that economic growth will kill us all as it does to a "liberal" assuming that government intervention will make things worse because government is the devil of the gaps.
If you were just talking about parties though, well I reckon that's because just as the left is so afraid of its own shadow that it concedes to neoliberalism at almost every chance it gets, the right is so afraid of the left's shadow that it jumps to support toxic populism and vested interests at almost every chance it gets. Commies have a lot to answer for.
We have a lot to thank classical liberalism for, it is the doctrine that gave us parliamentary democracy, which has been exported to nearly every single country on the planet. It was classical liberalism that was so fervent in abolishing the slave trade. It was classical liberalism that gave rise to the sublime idea that everyone was bound by the same laws, from the farmer, to the bishop, to the king.
That being said, classical liberals have lost or forgotten the moral foundations that underpin the movement. You hear classical liberals keep banging on about markets but none of them seem to understand why free markets are good thing. For these people, it is not the ends but the means that have become ends in themselves; we no longer make markets free to disperse wealth, and invite innovation, we make markets free to entrench the status quo and to strengthen vested interests. It's incredibly sad that many don't seem to understand this basic point. Even looking at it cynically, I don't think these people are advocating these positions out of malice, they truly believe what they say, but don't realise that they may be pursuing the right idea, in the wrong way. Adam Smith spoke of how avarice twisted the minds of men and would lead to the ruin of all society.
Markets are not, haven't been, nor ever will be completely free. Conservatives need to accept this and act accordingly. You can not have a situation where a government spends appropriated money on creating infrastructure only to sell that infrastructure at the fraction of the cost to a private individual who gains a cheap monopoly. Governments have been doing this for over a century and while they have seen the folly of this approach, the only possible solution left is to regulate the hell out of the market...which only distorts it further...which doesn't necessarily mean it's not justified, but certain consequences follow. The market is harder for new players to enter and innovate. We keep heading towards a society where breaking into markets is becoming almost impossible for those without large sums of capital.
Classical liberals need to understand that governments have helped to create big behemoth's of corporations and need to reign them in, by forcibly breaking them up. Corporatism is almost as dangerous a concept as big government. We are condemning entire generations of destitution if we continue to transfer wealth upwards, and we are in danger of creating the one thing that the entire movement was created to abolish, a de facto aristocracy.
I use markets as one example, but I can find examples in almost every single policy field available. If I keep writing I will probably go on forever, there are so many issues that I have uncovered with my side that it has actually gotten me depressed. I could never ascribe to the belief that society should be organised from the top down, but after having to gone to numerous meetings and seeing how the things I say get sucked into their minds as if the information were filling a vacuum and their eyes opening wide, I can see that we have a big fucking problem.
