You make a good point that it is good for consumers to be informed. But it is also a good thing for sellers to be able to price discriminate between high-volume and low-volume users, which is made possible by making more profit on the ink than on the printer. If they could not do this then printers would be more expensive than most people would want to pay, even though the cost of production is actually less. So there would be a lost opportunity from gains from trade, which results in decreased total social welfare.
But to reiterate, yes it would be good if we all knew how much cartridges would cost up-front. I've even heard of some printer companies (Samsung, if memory serves) selling printers with half-full toner cartridges, to make the up-front cost even lower. This gives consumers the (false) impression that toner will be cheaper than it is, on the thinking that "I just bought printer + toner for $80, therefore toner obviously costs much less than this". Unfortunately, this isn't true when it's a half-full toner cartridge.
As I recall, one of the endless antitrust-related suits that IBM was once involved with was a similar sort of price discrimination case involving printer supplies. "Overcharging" for supplies that you alone can supply is a very straightforward way to do usage-based pricing on products that can't easily be sold that way.
This is often called "metering" and I agree it can be a good thing if, for example, you are selling an experience good where people cannot accurately predict how much they will want to pay for it until they try it--it allows you to charge less up-front.
But I think in practice when you see this used in consumer goods sales, it's likely because the manufacturer is exploiting psychology in which unsophisticated consumers do not accurately predict their costs. For example: https://academic.oup.com/qje/article/121/2/505/1884013/Shrou...
IIRC most Ink Jet printers are sold with half filled "starter" cartridges. They have to, or people would just buy new printers each time because they're cheaper than a replacement cartridge.
