In the case of horses and cars, you need the same number of people to drive both (exactly one per vehicle). In the case of AI and automation, the entire economic bet is that agents will be able to replace X humans with Y humans. Ideally for employers Y=0, but they'll settle for Y<<X.

People seem to think this discussion is a binary where either agents replace everybody or they don't. It's not that simple. In aggregate, what's more likely to happen (if the promises of AI companies hold good) is large scale job losses and the remaining employees becoming the accountability sinks to bear the blame when the agent makes a mistake. AI doesn't have to replace everybody to cause widespread misery.

Yes, I understand that it's about saving on labor costs. Depending on how successful this is, it could lead to major changes in the labor market in economies where skilled workers have been doing quite well up to now.