system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5: Is there a legitimate reason why printers cannot print in black and white when one of the other colors has run out or are they just trying to sell more ink?
gpt
Not really.  The printer can certainly print a sharper black with the other colors, but it's not required.  As a couple others have mentioned changing the properties to grey scale should get it to print with only the black cartridge.

In almost all situations the best solution is to get a black and white laser printer.  They are durable, print faster, use far more economical cartridges, and don't dry out if they aren't used for awhile.  Really think about how often you honestly need color, for some it's important, but for most home office tasks a black and white laser is a much better investment.  If you really want color, there are color lasers, but you are back to the toner costing as much as the printer.