It's also pretty hard to measure the performance of software engineers at the senior level. When hiring, I don't feel like it's wrong to encourage good software

It's also pretty hard to measure the performance of software engineers at the senior level. When hiring, I don't feel like it's wrong to encourage good software engineers to refer former colleagues they think are good. I don't see why that would be wrong for C-level executive jobs either. It's really the same thing -- trusting the opinion of people you know and think are good is a better bet than drinking from a fire hose of job applicants of widely varying quality. At any job where your purpose is "leadership" and "impact" it is difficult to quantify success. People have tried to measure with things like OKRs, but ultimately a lot of what successful senior people bring to the table is hard to measure.