They used to be in some applications (like really big photocopiers). But toner is messy nasty stuff to deal with. Maybe refillable at a shop could work though.
I've been refilling the toner cartridges for my low-end Brother printer with generic toner off Amazon for years. It's not that bad and costs a fraction of the price of even a generic replacement cartridge. The toner comes in a bottle and you slowly pour it into the cartridge, perhaps with the assistance of a small funnel if necessary. I wear gloves and do it outside or in the garage. It only gets messy if you try to do it inside or have the dropsies. Obviously don't breathe it in.
They used to be in some applications (like really big photocopiers). But toner is messy nasty stuff to deal with. Maybe refillable at a shop could work though.