That’s likely because it’s unable to print the tracking dots[1].

1: https://en.wikipedia.org/wiki/Machine_Identification_Code

According to that article, the tracking dots only apply for color printers/printouts, so they wouldn’t apply in GP’s scenario (out of color ink).

OP has a color printer...? Do you instead mean to say that tracking dots shouldn't be printed in B/W mode?

I doubt that tbh - the wikipedia article above shows Reality Winner got caught printing (presumably) black/white NSA documents because the printer was able to print the color tracking dots.

OP wanted to be able to print in B/W mode when out of color ink. Ostensibly, the tracking dots' purpose was to stop currency counterfeiting, so they were only ever added on color printers (not B/W ones).

Therefore, not being able to display the dots shouldn't be an obstacle to the printer operating in B/W mode, as it would effectively be a B/W printer in that case. The more likely explanation is simply that HP wants to sell more overpriced color ink.

Interestingly, the Reality Winner documents were actually in color: https://en.wikipedia.org/wiki/File:NSA_Report_on_Russia_Spea...

So how does my b/w laser do this? :)

It doesn't, the origin of the dots is tracing counterfeit money and you can't do that with a black and white printer.

It actually uses some color for the grays. There are settings to force pure black and white but it’ll look more like a fax.