No "they" didn't. Wall Street is not a homogenous thing. You're thinking of banks in particular, which are about as different from hedge funds categorically as Facebook and Salesforce. Sure they're both tech companies with software products, but they have entirely different business models.
"[Melvin] was rescued with a $2.75 billion cash infusion from two other hedge fund titans, Steve Cohen and Ken Griffin. Cohen was Plotkin's former boss at SAC Capital Management. SAC shuttered after the firm pled guilty to insider trading and paid $1.3 billion in fines. Cohen was not personally charged. Griffin runs Citadel LLC ...
In exchange, Citadel and Point72, the successor firm to SAC, own an undisclosed stake in Melvin Capital Management."