There is a lot wrong with your argument. First, the attached article places the blame on concerns advertisers have with Musk dating to before he even closed the deal. Media Matters is only mentioned as having taken a poll. It is GLAAD and ADL that are credited with calls to action.
Second, no one who is serious, or understands BlackRock's business model, thinks they are coercing, or have the ability to coerce, anyone. What lever could they possibly use?