Community support & bugfixes. There's no real downside either, all printers that exist today are crap so it's not like they differentiate on firmware quality
They don't want long term support. They want printers to get old, drivers buggy and broken, and get thrown away so you'll get a new one with updated DRM. Ideally before the third party suppliers can really dial it in.
Even better if you have to throw away a few extra cartridges with the scrap machine because they don't fit the new one.
Just to be that guy: iOS/Mac users don’t have to worry about printer drivers or older printers working with newer devices. As long as you buy an AirPrint compatible printer. An iPad from 2010 that hasn’t been updated since 2011, can still print to a brand new AirPrint compatible printer. An AirPrint compatible printer bought in 2010 will automatically be recognized by a 2023 Mac or iOS device.
Your other point about DRM ink/toner is orthogonal to that.
Even better if you have to throw away a few extra cartridges with the scrap machine because they don't fit the new one.