In addition to Magnus’ points, I don’t think the cultural argument does it. It is much less well specified. Some people take issue that I define parliamentarism in the book as “executive subordination to the legislature” as too vague (I think it is clear enough, naturally). But if that is risking being too vague, culture is far more. In a sense, culture has globalized dramatically around the world—language, art, form of dress, food, family size, etc. You will probably argue that those are not the aspects that matter, but then shouldn’t it be the claim that culture is what matters to specify what aspects matter?
Some would say that the aspects that matter are issues like trust, low corruption, respect of property rights, etc. But are there any cultures which do not value those things, which claim they are outright undesirable? I don’t think there are. Instead, all cultures value those goods and would like to achieve them. If all do value those traits at least in abstract, does it make sense to call them cultural?
Unfortunately, their achievement of those traits is not conditional only on their desire to do so, but on the underlying incentives in the society. If you live in an “extractive society”, behaving like the most trusting Scandinavian person might not make you advance a lot.
A good parallel might be price controls (which are, incidentally, much more prevalent in presiential countries). In countries which do not implement price controls, prices achieve their equilibrium and business is trusted. But where countries do implement price controls, parallel markets are created, businesses are accused of cheating and of being excessively greed, trust is undermined. Many lament that the problem is that businesses are more greedy in the latter type of country than in the former. But the incentives are doing the real work.
Lastly, I would note that studies do control for long-term cultural aspects when they control for the region/country. One could argue that it is the shifting culture that promotes both parliamentarism and good outcomes, but the hypothesis seems to rely on increasingly ad hoc explanations, with the problem of being not very well specified already. When we add the evidence from e.g., American cities which have by and large the same culture, I find it hard to accept the hypothesis. At the very least, I think the burden should lie on the cultural hypothesis instead of parliamentarism.
Thanks, Magnus. You’re right, the argument involves many more elements which I did not explore in the post. I really like your summary and would invite all others to read the book (which is pretty short, and available for free as a pdf at whynotparliamentarism.com)