The Semiconductor Market Size was $503B in 2020 and is forecast to grow by 6% in 2021. Intel is the Semiconductor market share vendor leader with 16% share.
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A quick look at the microchip manufacturing world reveals a welter of companies with substantial market share. Intel and Samsung are well ahead (although of course this is chips across all devices, and many chip makers are specialised to certain devices), but there are a lot of others in the game.
There are basically just two phone OSes. It's all well and good to say you can just adapt Linux and make a new one, but if it were that easy, why doesn't anyone? I mean, that's the idea of how things are supposed to work: there are vast profits theoretically available, so people should be trying to get a slice of the action. Then why aren't they? The reality is surely that getting into the market is very expensive and difficult. Companies that might theoretically like the idea are taking a look and deciding it's not worth it.