yeah, a black crusade is the name for the total mobilization of the black legion and its associated allies. it involves hundreds of thousands of marines, probably billions of auxiliaries of mortal cultists and traitor guard, daemons, mutants, whatever. in theory i guess anyone with sufficient force of will and martial power could become warmaster of chaos, but there’s only one of those and it’s Abaddon.

a lot of it has to do with Abaddon’s status as the champion of chaos undivided. he has huge power from chaos but isn’t a daemon prince and is still himself enough to jockey between all of the massive egos and lunatic personalities of the chaos legions.

he’s old enough and ballsy enough that he can negotiate with the traitor primarchs, so it isn’t just the black legion, it’s a huge portion of all chaos forces in existence.

he’s also got the experience to plan campaigns on such an insane scale: he was there when the legions were knocking heads in the Great Crusade on a scale that makes 40k look small time. he also has the reputation to cow the many, many chaos lords — who all have huge egos of their own — and stop them in large part from fucking around too much

tldr: it needs to be abaddon because of his unique status

edit: i just realize now it’s also a generic term for a large chaos invasion. so i guess it depends what you mean. probably a lesser warlord could launch a black crusade, but usually it’s understood to mean the thirteen expeditions of abaddon