What do they do in all those hours?

My only experience with executives is the CEO at a "startup" (it really wasn't) in SF. He had to have his email password reset every week because he couldn't remember it. He was furious that asses weren't in all the seats at 9am, but he knocked off at 3pm on Fridays to go drink with his executive chums. I never saw any sign of leadership, vision, or actual work. Just demands on others.

what are they actually doing? what are the deliverables? are they actual doing intellectual work 12 hours a day?

At that level, they’re in the club and guaranteed to advance as long as they don’t make enemies and get kicked out of the club (which is rare, but happens, and usually means they spend a year or so finding another club.) So while some of them do work long hours, they don’t have to. They’ve already been judged to be in the in-crowd and could work 10 hours per week from wherever they want, and they’d still make every promotion.

So why do they work so much, and why do they go to the office? Because most of those guys (a) mutually dislike their families, (b) have psychological disorders, and (c) have office affairs. To psychopaths, 70 hours per week sunk into high-stakes office politics is fun.

Maybe they are "working" from a hotel downtown with their lover.