I don’t think it’s fair to say all MLs are like that. Mostly just the Stalin-leaning ones. Stalin and Trotsky were arch rivals and Trotsky was exiled pretty much as soon as Stalin came into power.

Trotsky and Lenin were arguably closer than Stalin and Lenin. However, throughout his life Lenin very much acknowledged their ideological differences and many of the Bolsheviks at some point or another had a “he’s never really been one of us”. Despite this though Trotsky was an important member and many of his writings became the official party ideological line on a large variety of matters.

Because Stalin won and Trotsky was exiled he just kinda got the right to claim his ideology as the “real” Marxism-Leninism while Trotskyists will go on and claim that they’re the real heirs to that ideology and both sides will accuse each other of revisionism lol. But Stalin was much more of a practical person than a writer. He was even occasionally teased by other members of the Bolsheviks for his lack of erudition. Not that he was dumb by any means. Just that he wasn’t nearly as steeped in theory as the rest of them. He was focused on getting shit done, not getting shit right

My personal view is that Trotsky definitely had a habit of straying pretty far from orthodox Marxism, but Marxism-Leninism is also differentiated from orthodox Marxism in the ways that it had to grapple with elements unique to Russia that the Western theoreticians didn’t have to face as much (e.g. the unique and critical role the peasants played in Russia). The history of the development of Marxism in Russia is basically a constant effort to adapt the theory to this landscape.

Sometimes the difference is really just in practice too. Like one major marker of Trotskyism is that he wanted to begin collectivization of farms early on (note that the party had briefly tried collectivism but had retreated with the NEP to allow some markets for a while) whereas the MLs around Stalin argued they should wait until the party was stronger. In fact this was one of the main issues at the core of the argument that eventually led to Trotsky being exiled. Funnily enough Stalin resumed collectivization efforts very soon after that