There's a lot to your reply, much of which I agree with and some I do not, but we cannot afford the space or time to expand this much :).
Trying to keep this brief, I think the issue is a matter of scale. Many of the roles or professions you mentioned do not really scale the same as software products do. One might argue that a farmer scales food production, but that is largely a solved problem which can almost be completely automated away. Taxi drivers and other laborers generally only provide 1 person amount of production value. Software engineers take idea from others or themselves and produce things which typically scale up very well. And because that process of taking an idea and producing working software is as much an art as a science, it is not easily replaced. Thus it has somewhat outsized value.
> Key employees whose departure
I strongly suspect that most key employees leave or are released without the company recognizing their importance. I don't believe this has anything to do with software developer salaries. Now the CEO level has successfully led everyone to believe that huge compensation is necessary to retain their special talent (talent which somehow exists even when companies have poor results); but then, executive boards are often staffed with other CEOs.
> So why are hardware engineers so much worse paid than software engineers
What they produce is far less consumable. They make tools or appliances (incredibly complex ones, but still). Software is ever growing and changing. Perhaps in an ideal world we could figure out what we need before writing the code, but it rarely goes that way. And since most businesses don't really understand their markets until they get into things, and consequently need to adapt and change to suit their market, the software has to adapt as well. The hardware isn't changing in most of these cases.
One could argue that software is a consumable in this regard. Certainly with the modern startup approach, software is built in stages and released at each stage, "finished" or not; then it is amended, updated, etc. Hardware just doesn't do this as much. Even with firmware updates (which are software...), it is often possible to ignore them and use what you currently have as long as it suits your needs.
Trying to keep this brief, I think the issue is a matter of scale. Many of the roles or professions you mentioned do not really scale the same as software products do. One might argue that a farmer scales food production, but that is largely a solved problem which can almost be completely automated away. Taxi drivers and other laborers generally only provide 1 person amount of production value. Software engineers take idea from others or themselves and produce things which typically scale up very well. And because that process of taking an idea and producing working software is as much an art as a science, it is not easily replaced. Thus it has somewhat outsized value.
> Key employees whose departure
I strongly suspect that most key employees leave or are released without the company recognizing their importance. I don't believe this has anything to do with software developer salaries. Now the CEO level has successfully led everyone to believe that huge compensation is necessary to retain their special talent (talent which somehow exists even when companies have poor results); but then, executive boards are often staffed with other CEOs.
> So why are hardware engineers so much worse paid than software engineers
What they produce is far less consumable. They make tools or appliances (incredibly complex ones, but still). Software is ever growing and changing. Perhaps in an ideal world we could figure out what we need before writing the code, but it rarely goes that way. And since most businesses don't really understand their markets until they get into things, and consequently need to adapt and change to suit their market, the software has to adapt as well. The hardware isn't changing in most of these cases.
One could argue that software is a consumable in this regard. Certainly with the modern startup approach, software is built in stages and released at each stage, "finished" or not; then it is amended, updated, etc. Hardware just doesn't do this as much. Even with firmware updates (which are software...), it is often possible to ignore them and use what you currently have as long as it suits your needs.