It's simplistic and lacks nuance. Russia in the spring and early summer is very muddy, and would slow down an invasion more than the winter, and autumn turns to winter very quickly, so there's only really about a month and half of the year that you could actually "invade", but it is borderline impossible to actually organise and carry out an invasion of such a massive country in such a short amount of time.

It's spoken by a lot of these guys as a Truism rather than an actual examination of Russia's material conditions.

The problem with (not) invading Russia in the winter is twofold really. It's so damn cold that invading during winter is a bad idea, but that's true to a lesser extent just about anywhere. The second problem is that Russia is so goddamn massive that you can't reasonably invade all or even part of it before winter sets back in. Operation Barbarossa started in June

I think it goes back to the idea that liberals and fascists believe that the Nazis only failed to conquer the USSR because of the winter, not because of the superior Soviet society they were attempting to destroy. What these modern geniuses fail to recognize is that the Soviets also had to deal with that winter, and unlike the Nazis, they did so successfully.

I mean the most famous case of a successful invasion of Russia is the Mongols, who did in fact invade during the winter. So that "advice" only works in specific contexts and times, it's not like some self-evident Fact like these folks love to parrot.