if they're both paid the same hourly rate?

That's the fun part: you only have to pay them for 40 hours!

You just aren't thinking like a billionaire, man. What you do is get the two people anyway, and still force the 70 hour work week.

Your job is not to find a reasonable steady state of operation. Your job is to exploit the resources before you (even the ones with emotions and families) to extract value for the shareholders in the most efficient way possible, before somebody even more evil and clever than you figures out a better way and we direct future fresh meat to his meat grinder instead of yours.

Benefits can be expensive, and they only pay you for the 40 hours because it's a salaried rather than hourly position. They just want free labor at the expense of the employees' sanity.

Insurance, benefits and labor expenses. Even in places with little worker protections there are costs that scale with the number of workers instead of the number of hours.
A brief look indicates employers in India can expect to budget on the order of 18% of an employees take home per year for those expenses.

There are some circumstances and places in the US where you don't need to provide as many benefits to employees who work below 40 hours. Then you see employers hire more people and schedule them for just under the threshold to give them benefits.

The answer is always because it's cheaper for them somehow.

Overworked peasants have neither the time nor the energy to revolt.