How does any business that operates machinery have so many employees? If your core business is machinery that stamps metal into widgets it does not follow that you need one guy to turn the machine on at 9am, then off at 5pm. You need to design them, you need to repair them, you need to update them, you need to clean them, you need humans to react every time something unpredictable happens. Then once you have more than a handful of employees, you need hr, bookkeeping, office maintenance, and management to coordinate all that.

Also, a business like indeed is going to employ a huge number of salespeople to sell listings and recruiters to try to fill them. Regardless of what you've heard, websites are not magic money machines that effortlessly operate at a profit once built. They are just a way of interacting with your human customers who still bring all the issues human customers bring.