No, it's that material conditions restrict choices, so an analysis of them is needed to chart the right course. Marx is explicitly developing his theory not just as a description but as a method of deciding action.

It's not dogmatic and ultra-determinist, it's dynamic, changing, with ideals and material reality in a constant, mutually altering tension and flux between the world as it is and as it will be, and how the world as it is alters our desires for how it should be, and vice versa.

Masses and individuals have a great effect, but their power isn't infinite, and what they want is also contingent. And until you know how the current society arose from the interaction of material reality with people's desires, you cannot see the avenues where positive change is possible, the avenues that lead to a worse outcome, and those that lead to dead ends.

EDIT: one thing is to remember Marx is developing this in contrast to Hegel. Whereas Hegel says the "Zeitgeist" determines the course of history, Marx says it first arises from history, then alters it.