Inkjets are complicated, hard to get right and companies that make them have to hire electrical engineers, software engineers, firmware engineers, hardware engineers, mechanical engineers, chemical engineers, experts in microfluidics and more. Not to mention, I bet a lot of stuff is protected by patents owned by HP, Funai, Xerox and Epson to mention a few.

Add to that, the market model is mostly a "razors and blades" model where you sell the hardware at or below cost and charge more for the ink and everyone hates you for it.