I’m a big proponent of open source hardware but as your post shows it often involves skills of many disciplines that requires vigorous thought or trial and error. Electronics and physics are unforgiving in a way processors are not.

Even after reaching the prototype phase, the open source hardware is probably only useful to one person: it’s creator.

There is a big difference between making a prototype and detailing the build in sufficient detail other hobbyists can replicate it / modify / use it. Documenting hardware is substantially harder than documenting software. If the project is cool a bunch of people will be excited to jump in; some of these people have zero experience soldering or ordering laser cut parts or whatever. Supporting them is hard.

Then another step up to sell the design to other hobbyists, even just a few extra copies on Tindie.

And then a huge step up from that to selling to the general public, where suddenly FCC interference certifications are needed and the company is liable if the design burns down a few houses. There’s a reason firms making hardware have real engineers on staff held to professional standards. Plus all the cash flow and business concerns when the marginal cost per unit isn’t under 1 cent like software.

Each of these steps often involves multiple iterations of hardware and therefore lead time and cost.