Marx is popular because his first volume divides people into the good guys and the bad guys by cleanly separating classes so everyone who hates their boss or landlord is quick to agree with Marx. Even Marx himself doesn't believe everything he wrote in the first volume, in fact, most of the good answers and thinking are actually in the third volume which nobody including me has read. The parts that I have read could have come out of my mouth with only minor modifications.

Stalin had only read scraps of the first volume, the one that divides people into good and evil, the one that doesn't actually try to find the underlying problem, it was only natural that he was doomed to failure. Imagine being wrong while fully believing your cause to be infallible.

The problem with Marx isn't that he is vague, it is that you have to read 2700 pages of difficult to read text which nobody, not even the staunchest supports have done. Why? Because it would take more than 160 hours to both read and understand what he has written. You may have to reread it twice because the third volume gives you a new context for the first and second.

Marxism is doomed due to bounded rationality.