You're assuming it would be more productive overall. I honestly doubt it would be more productive to work 30 hours than 50 (more than that and there probably would be more signs of problems). And I don't know where you're getting 120 hour work-weeks in my post, because I never suggested that. Wakshaani is saying 72 is closer to the norm for drones anyways. It isn't like the megacorporations want you to enjoy a few decades of retirement on their dime; they'd probably be happy if by the time the wage-slave retires they've got a bad heart and will die within the decade (rather than three of them).
The real goal of the megacorporations isn't to make people work that hard. That generally involves things like compensation or pushes them to their limits in a negative way. The real goal is to make them want to work that hard, motivate them to push themselves to the limit. Sure, the job 'requires' 40 hours a week. But everyone in the megacorporate culture knows that's 'slacking.' And if you're slacking, someone more dedicated and productive than you will come along and take your job. And if you want to get a promotion, you better be working harder than the people above you, otherwise you obviously don't deserve their spot in the hierarchy. You know you're only getting paid for those forty hours, but if you don't want to lose that job, or if you want to get one that pays you better for your time, you have to put the work in. One day, through sheer hard work and determination, you could become a manager.
Now, real secret behind this is that in a dystopic megacorporate future, there's a glass ceiling somewhere in there with very few holes; those holes are there to relieve pressure and let the higher-ups say 'see, you CAN work your way to the top if you try!' Most people won't actually advance that far. The few that do are either phenomenally good or are side-lined into something that doesn't really matter after their promotion ceremony was used for the propaganda that it is. The majority of your management and higher-ups would have been hand-picked and groomed for those positions or acquired from other sources. They just make it look like you can advance so you'll put as much effort into pleasing them as possible. No kid will jump for the cookie hanging twenty feet in the air. But if it dangles enticingly just out of reach, you'll have those kids climbing over each other to get at it. Then you lower the string once in a while, a kid manages to snatch it, and all the other kids know there's a chance they get a cookie too, because they can see the crumbs all over that kid's face.
Even wage-mages have to deal with this, because while they're rare, they're not that rare. There's about as many competent magic users around as doctors or lawyers, per million. Sure, you can't just train anyone to be a mage (not that everyone you'd try to train to be a doctor or lawyer would succeed either), but recruiting is as easy as going to a slum-school, assensing all the kids, and making scholarship offers to the ones who ding on your magical radar. Not all of them will accept, or even pass, but some will. It takes a little more time, but the loyalty is much better (given you're saving them from poverty and other problems of living in a slum, it is somewhat built-in). And now there's competition between those wage-mages. It isn't as much about the risk of losing your job; it is more about the opportunity to get a better one. Having magic doesn't make you immune to wanting to improve your position and secure more pay, more rewards, etc. It's a competitive megacorporate culture, after-all. Do you want to be the lackey summoning test spirits until you almost pass out from Drain every day, the mage who uses assensing to supervise and record the results of the testing, or the boss who is getting all the credit for your hard work and going on a cruise-liner in the Carib League as a reward for it? You don't want to be the first one, do you?
Burn-out/exhaustion is totally a thing that can happen to higher-ups anyways; one of the main kinds of extractions is the rich, well-paid wage-slave who is unhappy with his workplace paying you to get them out of there.
Another facet of the dystopic megacorporate culture to remember is that your happiness and comfort are not priorities, ever. Your efficiency/productivity is what matters, and if giving you a vacation once in a while is what boosts your productivity, that's what they'll do. If drugging your tap water with drugs to alter your mood is what will boost your productivity, that's what they'll do. If holding your family hostage is what will boost your productivity, that's what they'll do. If you aren't worth it and someone else is, they'll drop you out of that position and replace you. You're not a person, you're a tool, a cog. If you aren't running perfectly, they might apply a little grease or file off some rough edges for you; or they'll flat-out remove you and replace you with a better part. Getting a new cog and gears is easier than maintaining one that is past its prime, and if you're a more special kind of tool, maybe they'll keep you going a bit longer. Once you can't keep up, though? Once you tip the line between cost-effective and a drain of resources? Either you're going to be fixed or gone.
