It's impossible to quantify how many people were killed by an economic system because it's never direct. You would have to arbitrarily decide how many layers of abstraction are too many for the death to be attributable to the economic system under which it occurred, and the more layers there are the more unclear it is. That's why the "victims of communism" numbers and lists that get thrown around are all bullshit, it's entirely subjective. If you want to be objective you have to be specific about the cause of death and whose actions directly resulted in it.
For example, imagine an alcoholic homeless man dies of exposure after being evicted from a building he was squatting in. Who's responsible? There are lots of answers you could give; the cops who were sent to evict him, the owner of the building who sent the cops, the community who didn't help him, the person or company that sold him the alcohol, the alcohol itself, or even just himself. I can't objectively say that this man "died by capitalism," but I can say that it might have been prevented under a different economic system, that this is a systemic problem that requires a systemic solution.
Millions of people are saddled with bills they can't pay and an uncaring and complicated bureaucracy they struggle to navigate because of poor education, then they find a community of people claiming to have the solution to all of their problems. It doesn't have to work, they just have to believe it does and they will rationalize away any sign that it doesn't. The sovcit community gives them a feeling of autonomy and control they will not easily part with.