Porky and the PMC can't stand the idea of their workers not being completely under their thumbs.
If you work from home, the work gets done, but you might also be doing something like reading a book, or watching Netflix while working. You might be working in casual clothes, or playing with your cat.
In an office though, Porky has control. They can dictate everything, police everything. Make sure every minute has you working, police your clothing choices, force overtime, force office team building events. The PMC thrives on control.
Remember, being paid minimum wage means that they'd pay you less if they could get away with it!