It's all about marketing.
If you see a printer that takes your eye and the price is really low, you will buy it. Now that you have bought it, you will indeed buy ink for it.
Sell the printers at below the cost of manufacturing and soak the consumer for the ink.
Most brand name printers now come new with cartridges that are not full of ink, they print approximately 1/3 of a new retail, or refilled ink cartridge.
By far the cheapest way to do lots of printing (with a inkjet printer, not sure about laser) is to refill your own colour and black cartridges. If you buy ink in bulk, say a liter, or quart of each colour you can buy all you need for the price of a new cartridge, that will fill them many, many times. Most cartridges with work fine for at least ten refills providing you do not let it dry out when empty. Refilling is cheap, a bit messy, but cheap.
Some people do buy a new printer each time they run out of ink, that too can be cheaper, but that is why they are now selling without full cartridges.