Mind that planned economy was not a Marxist institution or invention, rather, it was a carbon copy of the economic system of the (conservative) Germany empire in WW1, which had shown some impressive production rates. (In fact, these have never been achieved again.) There had been several attempts to copy at least some elements from this, all over Europe, in the inter-war years. (The Royal Navy, on the other hands, claims the fame for the first truly standardised and interchangeable product, rigging blocks. Mind that this kind of standardisation requires elements of planned economy, as well, and is also a prerequisite to any fully planned economy.)

Moreover, while John Stuart Mill described some kind of a market place inside factories, the advent of management soon brought the concentration of all manufacturing knowledge in a central representation, where it was dismantled, reassembled and redistributed to the various work stations. As compared to Mill's description, a Fordist factory already represents a planned production process. The idea of extending this beyond individual factories (and at the same time gaining some control over the antagonistic forces that dominated the economy) was somewhat natural and not that revolutionary as we may think. Another root may be the central planning and commissioning of roads, bridges and railways – and thus of economic development along those routes. It is not a coincidence that Charles Joseph Minard (who was quite in alignment to the Second Empire), who's famous charts already remind of the kind of knowledge required for a planned economy, had been General Inspector of Roads and Bridges in France.

(Meaning, while soviet planned economy was radical, it was by no means alien to the general development of economy, it was rather an extension of what we would now call conservative policies. The very idea of policy (as in "Policey" as a means of increasing the efficiency of a national body by general directives), is a conservative one. Therefore, it shouldn't come to much surprise that we find commonalities in both of them. Just because we find an elaborate state of planning in, say, a US manufacturing process, it doesn't mean that this is Marxist, nor does it mean that the EU is a Marxist conspiracy.)

Europe's experiences with untethered capitalism in the 19th century had been generally problematic, and it had waddled from the great crisis of the late 1920s and early 1930s directly into the war, now facing enormous efforts in reconstruction and redevelopment. The idea of doing better, this time, wasn't totally unconceivable. Especially, since European powers were also facing a significant loss of power and influence in general, and thus also limited economic prospects. (Even the first program of the German conservative party, after the war, declared untethered capitalism and Marxist economy as failed in equal ways, giving rise to what became the predominant model, social market economy, which met with analog concepts popular among social-democrats.)