If the recent revelations in the Epic vs Google court case are anything to go by, Motorola is likely getting paid by Google for every single Google search and Google Play Store transaction that occurs on that phone. It could even be sold at a loss. I don't think pointing at a low-cost smartphone is a very useful point of reference given that context.

However, I think there are plenty of Linux SBCs (single board computers) that have 4GB of RAM for around $50, just no screen, GPS, cellular modem, cameras, speakers... all sorts of things that add cost to a cell phone. $10 is a far-fetched claim, in my opinion, and citations are needed. The Pi Zero 2W is $15 and only has 512MB of RAM. So, sure, let's go with $50.

Have you considered how cheap printers are? I see multiple inkjet printers on Amazon that cost $59. Adding $50 would nearly double the price of the unit. Other manufacturers would eat their lunch, so you can see why no one is rushing to offer a $59 printer with an additional $50 worth of computer built in. Even if it were "only" $25 extra, that is still significant.

At the higher end, printers do start to include more of everything, but those aren't the printers the average consumer is buying.