This is because even replacements are produced according to generally accepted standards.In contrast, cheap printer toners can be released for sale by companies that can reduce the cost of their production or be covered by some kind of promotions or rebates.
On the other hand, it can be said that it allows the sellers themselves to acquire new customers.
Laser printing is an electrostatic digital printing process.It produces high-quality text and graphics (and moderate-quality photographs) by repeatedly passing a laser beam back and forth over a negatively charged cylinder called a "drum" to define a differentially charged image.1 The drum then selectively collects electrically charged powdered ink (toner), and transfers the image to paper, which is then heated in order to permanently fuse the text, imagery, or both.
As with digital photocopiers, laser printers employ a xerographic printing process.However, laser printing differs from analog photocopiers in that the image is produced by the direct scanning of the medium across the printer's photoreceptor. This enables laser printing to copy images more quickly than most photocopiers.Źródło: https://en.wikipedia.org/wiki/Laser_printing.