Lots of <i>things</i> are just Android devices. This allows their manufacturers to easily hire people who is comfortable developing on a known platform, and also repurpose very cheap obsolete hardware that couldn't run a modern phone but would still be usable for a stripped down OS that runs only one app. And of course by being hard+soft solutions they can charge a lot more compared to a simple "normal" app.
All good from a business POV, but most of those devices are tight closed with locked bootloaders and other protections against repurposing, which turns them into e-waste once their services are terminated. Pollution issues aside, an old board that runs only Android 4.x is pretty much unusable for everything interesting, while being able to unlock the same board and install Armbian, DietPI or similar OS, turns it into a completely different device.