Besides, people trade compensation for all sorts of things: working at a nonprofit, working in their rural hometown. Why shouldn't problem domain be one of them?
This is not limited to software engineers. I believe the same is true for any worker, from fast food to manufacturing to engineers.
That's easy to measure. These companies have a per-employee revenue which is easily a 5-10x multiple of average total compensation paid per employee, and in some cases it's also much less than the per-employee profit.
So they could pay a ton more while also making a healthy profit. Apple is the worst example of this.
However, in today's economy the situation you describe would have the workers being paid less and the owner trying to keep as much of the surplus value from their labor as possible.
So, even in a failing company, I'd expect the wages to increase for workers if they received 100% of their value.
and this is how gentrification works. Not because a company starts to pay less, but because other companies pay more and make just the act of existing close to those companies (even if you were in fact there first) more expensive.
Your solution is great for tech workers, but ultimately means a large swath of society would suffer.
And you might not know this but "charities" & "ngos" are notorious for bad pay and working conditions