Because if (when) the markets crash by 40% and show no sign of recovery, salary will remain a lot more constant than total comp.

Seriously markets only go up (and the absurd inflation of tech company stock prices since 2008) is a deep, deep problem with society which will inevitably end.

That's not the point.

Companies exist to reward their shareholders. Employees at most companies get paid as little as possible, as long as they don't quit. At tech companies, employees are shareholders and therefore they get to be part of the group of people that the company exists to reward.

If you approach your stock compensation with that understanding, you'll be fine. If you expect the stock to only ever increase in value then you are being stupid. In my experience, tech workers at public companies are pretty savvy about their stock compensation. At startups, it's another matter...

But the question was why one would report salary rather than total comp. I provided a potential answer to that question.