I’ve never forgotten Frederick Copleston’s blunt take on Marxism’s 20th-century success in volume 7 of A History of Philosophy:

[Marxism] is accepted, doubtless with varying degrees of conviction, by a great many people today.  At the same time it is arguable that its continued life as a more or less unified system is primarily due to its association with an extra-philosophical factor, a powerful socio-political movement, the contemporary importance of which nobody would deny… [I]t is the Communist Party which has saved Marxism from undergoing the fate of other nineteenth-century philosophies by turning it into a faith.

Or to be a little more blunt, Marxist philosophy was a classic “senile industry.”  Massive government patronage kept employment and output high decades after the disappearance of most of the sincere customers.  Marxism didn’t just justify “conspicuous production” of white elephants.  It became one.