West State Logistics isn't a high-tech firm with complicated tasks; even if these people aren't perfect, they can still be reluctantly used like beasts of burden.
A thousand Dollars a month, the cost for many American small capitalists to hire undocumented immigrants isn't even this low!
Replacing over two hundred mid and lower-level management positions with prisoners can alleviate costs by over five million Dollars a month—the cost of labor isn't just limited to wages; in America, the direct wages given to employees are even a smaller part of the cost of labor.
Business insurance, benefits, taxes, administrative expenses, there are just too many expenditures beyond wages.
If you think Sheriff Gru's problem-solving approach is that superficial, then you're underestimating him; after battling with heroes for so long, even if Gru were a pig, he should've evolved into the king of the pigsty by now.