It strikes me that open source hardware should be more common. It's surely much easier to monetise than open source software: you just sell the hardware, because noone wants to build one themselves. Why isn't it?
Because hardware is, well, hard. There is a huge upfront investment that isn't even remotely comparable to the amount of money you can spend on software development, and equally huge incentives for third parties to undercut you by taking your designs, manufacturing them for cheap and offloading support onto you (as already pointed out Arduino is a great example of this happening in real life). Even if everything is open source you have to build an entire business and marketing department around selling the hardware, while with pure software you can just put it up on GitHub and call it a day.
Not to mention that in this day and age every piece of hardware has software at its core, so open source hardware does not save you from also writing the code that runs on it. If anything developing open source firmware is actually harder, because most chip vendors expect your product to be closed source and want you to sign countless NDAs before you can access a datasheet or even just buy the chips. You are restricted to using older and/or more expensive parts whose documentation is freely available; it's the exact opposite of the software world, where the latest and greatest is one npm install away.
No one wants to built it themselves until people actually want it, if your device is popular then your device is $2 on AliExpress/eBay and you have no part in that, look at Arduino for a good example.
This...if it's successful, a knockoff of your device will end up on eBay, AliExpress, Amazon, etc, often with sketchy parts, at a price you'll never match. With some exceptions, where you're able to make the product depend on a hard-to-get-cheap part, etc.
Just from reading comments and articles, I’d guess that’s because you very often rely on 3rd-party parts that are not open. So you either need to limit what you use, or design the whole thing.
