Hey there! Hello!
There are many reasons (some of them quite specific) why a company may choose to get workers from foreign places. Some of these reasons include being able to say they have a broader range of global knowledge and leverage, gain access to more market areas, and giving more difficult/time consuming responsibilities to external agencies while they focus on core business processes.
Some of the most common reasons, however, is a company's interest of cost and mitigating risk. It's significantly cheaper in operational/labor costs to outsource, and workers are less in the hands of the business, making their reliability go down. It really seems like a win-win for big businesses.
Hope this helped you out! Feel free to ask me any additional questions you may have.
–Lamb :-)