Imagine that c-suite types may just work for the salary, too, like many of the fellow engineers among the readership of this site. They care about the mission, but they also care about making enough money to support their other obligations (like family and kids) and tend to choose a well-paying place when they can. They try to sell their skills and knowledge not very much below the market rate.
Let's say: hey engineers, how about cutting your salary to $60k? It's close to the US national average, it should be "enough". If you think $60k is too little, ask your colleagues from EU, from India, to say nothing of Africa.
I bet some very mission-driven engineers will remain. But a lot would eventually leave.
Same applies to a lot of values of x in CxO. And you do want highly qualified people there.