As you probably know, Rate L is offered to customers who consume very large volumes of electricity, generally for industrial activity. Their electricity bills are therefore much higher than those of residential customers!
The price of electricity on your bill can’t really be compared with the wholesale prices offered to industrial customers. As is the case with most consumer products, wholesale prices are lower than retail prices. It costs less to supply a large quantity of high-voltage electricity to a single location than it does to supply the same quantity of low-voltage electricity to tens of thousands of homes.
It’s also important to remember that hydroelectric power generation allows Hydro-Québec to offer residential customers the cheapest rates in North America.