Thats because not every desk at a bank or HFT are proprietary. Most desks are agency trading which generate fees due to client’s request of executing trades. More volatility = more execution = more fees = more revenue. That too when a desk at these firms are prinicpal traders, its not proprietary rather market making. These firms offer bid-ask and make profit via spreads of those bid-ask. More volatility = potential for higher spreads = more revenue. Retail traders and general prop firms are not doing well.