Hustle culture is a form of CYA for poor managers. If I, incompetent manager, hammer on my employees to hustle, I can claim I am doing my best to manage my team and any deficiency must be their fault because I've set the standard.
Nevermind that every job is different and the outcomes are measured very differently and sometimes "hustling" or "staying busy" is actually a substandard way of achieving most tasks consistently as the short term benefits of hustling give way to burnout.
Bad managers are asking employees to constantly sprint when business is a marathon. It's a weak form of leadership generally ascribed to the "professional" managers with (only) business school backgrounds who can't understand what their employees actually do nor understand the system of the company as a whole.
It's a classic short term quarterly profits mentality.
Employees have for centuries been doing this sort of thing. Looking busy by optimizing for busyness over actual productivity because they realize managers are only concerned with looking good and skating by, not the actual business outcomes.
Note for those starting a business: design your corporate structure so that middle managers incentives are visibly aligned with the actual success of the company and not with visible working culture. And then set the pace properly.
A motor cannot work at 100% duty cycle and maintain it's longest possible service life before being rebuilt.