alt Hacker News> Only speaking for myself, but the problem with Android is that it and the hardware needed to make it run acceptably are absurd overkill for the use case, which drives up cost, cuts down on battery life, and adds a layer of unnecessary complexity (suddenly you need to think about what player app to use, for example).
The battery life is fine on modern DAPs. Excellent, even.
I understand why an engineer would want a completely application specific, built-from-scratch OS that does one thing perfectly, but that's a pipe dream for a niche market.
A powerful and efficient SoC that runs Android is ultra-cheap these days. Less than $1. Hiring an engineering team to write and maintain a custom OS for a niche product would incur so much R&D cost that it would wipe out any money you'd save by using a smaller microcontroller and drive the final cost up.
Just think: How much salary would you have to pay a team of engineers to write the custom OS and maintain it? If you could optimistically sell 500,000 of these devices (good luck) then how much would you have to save in order to pay for the R&D?
You don't need "OS" to play some music, drive display and talk via USB/BLE. It's trivial task and could be done with a few event loops. A lot of firmwares is being written without OS. May be FreeRTOS/Zephyr to somewhat simplify the programming, but that's definitely not "OS" in a commonly accepted sense. You don't need team of engineers, one hobbyist could easily do that. I wrote firmware for a device of similar complexity (work with ADC, implements USB, BLE, some UI with buttons and leds) and I'm not even a professional.