>The USPS as a whole operates at a loss, why couldn't junk mailing be operating at a loss?
Because there's no earthly reason to take a loss on advertising?
What you're not accounting for here is the cost to pick up individual envelopes from your house, and the cost of dropping a presorted bundle shipped to the BMC into the truck.
Much of how the USPS operates, including how much they charge and what services they offer to other businesses, is mandated by Congress. They don't have any choice.
Because there's no earthly reason to take a loss on advertising?
What you're not accounting for here is the cost to pick up individual envelopes from your house, and the cost of dropping a presorted bundle shipped to the BMC into the truck.