If you put 90% of the electronics into the cartridge and the printer box is just a paper feeder - that's not exactly surprising.
"Just" feeding paper is extreme engineering. And a disposable vape has more compute in it than a toner cartridge. (Though there is insane non recurring engineering in an inkjet cartridge. But I bet just the warehousing of a printer is a significant part of the total cost of a printer.
HP retail ink cartridge prices are not a cost issue.