Is startup CEO's job to work “in the shadows” and be mysterious?

I have worked in couple startups (20-50 people), and it always seems like the CEOs are the mysterious figure, and no one really seems to know what they do on daily basis.

The CEO would be out of office for weeks and sometimes pop in randomly and get going again. They would normally give some kind of random speech/update every couple months, but other than that you wouldn't really hear or see them directly.

So is this the norm? What are the CEOs working on?