reasoning: you're using indentured trafficked workers trapped in homes (and possibly also fraudulently claiming housing benefits) to grow an illegal product. Electricity will be a significant cost (in the UK, at least) and so stealing it makes more sense.
Certainly in the UK this is the case - people are smuggled into the UK, and have to repay the cost of being smuggled by growing cannabis (or sex work, or similar). Passports are removed, fear is created about going to police, people are locked into houses, etc.
