The problem extends far deeper than just FOSS for mobile and IoT. There isn't competitive OSHW. The entire pipeline for silicon hardware development (PCB dev is relatively easy) is virtually locked away behind gates that require identity and/or address verification, node-locked trial licenses or sometimes big license fees paid to one or more big 3 EDA vendors. And that's even before getting anywhere need talking to a fab.

This.

If memory serves me right, in early days of Android, Google engineers were writing drivers on behalf of manufacturers because OEM drivers were too buggy.

Think about the amount of work and the kind of talent this requires.

If you are starting from scratch today as a no-name company, I doubt any hardware manufacturers even want to talk to you.