The consumer pays for all the costs of a business!
They like to know they are getting money to spend rather than risk you not paying when the bill arrives and them having to borrow to cover your debt and pay the collectors, etc.
The actual rate of interest they can earn on your cash is quite low compared to the costs if you don't pay.
Maybe you could get a better deal by paying 3 months in advance? Or how about a smart meter and paying daily or by the unit?