They are required by law to do certain things. You can't print black if yellow is out because the tracking microdots won't print. The region is extremely important not to be changed because different regions have different requirements.
You can't even create a printer startup and fix the issues because it's all basically regulatory.
I do not believe that a colour laser printed can't switch to whatever tracking dots mono laser printers use when out of yellow ink. I'd believe laziness over compliance issues.
Citation needed about tracking dots on B&W lasers. I don't see why they're necessary: the main reason is for anti-counterfeiting. B&W lasers can't be used for printing counterfeit money, for what I hope are obvious reasons.
I don't know if they have them - but the same argument still applies. If you're printing in mono then no tracking dots are necessary, therefore stop complaining about missing yellow ink.
Printers are mechanical devices. Putting ink on the page in a way that actually looks good requires quite a lot of precision. It may take a lot of resources to get a marketable product, so it’s not something startups tend to do.
You can read more about how the eff has determined that 'all major printer manufacturers have a secret agreement with governments to implement tracking'. There's no link to the specific agreements though since they are secret. It's just known that printers add colored docs to track documents and it's also known that this is required by various governments throughout the world.
You can't even create a printer startup and fix the issues because it's all basically regulatory.