Why are Android and iOS the only dominant mobile operating systems?

The biggest barrier is the ecosystem, not just writing the software. Android and iOS already have huge app libraries, developer tools, hardware partnerships, and millions of users. A new system would need to attract users before developers, while developers usually wait for a large user base first. That makes it extremely difficult to reach the same scale, even if the core operating system works well.

Android itself is largely open source and uses a modified Linux kernel, so it already fills much of that role. There are also alternatives such as Ubuntu Touch, Mobian, postmarketOS, and other Linux-based mobile projects. The main issue is that supporting phones requires more than an operating system: projects need hardware drivers, power management, cellular support, camera integration, app compatibility, and regular updates for many different devices.

There are open-source phone operating systems, but most support only a limited selection of devices and may lack polished features such as reliable cameras, banking apps, games, or carrier support. GrapheneOS is another example, though it is designed as a privacy-focused Android variant rather than a completely separate mobile platform.

Creating a phone operating system is also expensive because manufacturers and carriers control much of the hardware and certification process. A desktop Linux distribution can run on relatively standard components, while phones rely on highly customized chips and proprietary firmware. That technical and business overhead is why smaller projects tend to remain niche.