TrueDuality parent
You don't necessarily need on-package RAM for this. I'm not sure I'd build a project around this, but 16MiB of RAM would hardly be BOM killer.
Actually it is. If you want to build a cheap sensor or actuator, than any additional component is getting expansive. Remember it is not only the external component, it is also the PCB space, is the production, and the testing after production. This adds up all to the costs.
When you use a µC to make it cheap, then you don't want to use additional components.