Or they entered on the country on the US Visa Waiver Program or similar programs in other countries, which is surely the most common way to travel between first world countries (apart from inter-EU travel, which is more permissive again) and allows you to travel either for tourism or for business.

Yes, I would assume those executives get business visas where required, just as I do. In addition to meetings and conferences, those visas at least implicitly allow for continuing to do whatever is required for their "day job" back home.

But mostly, US and EU citizens in particular have visa waivers or, at most, a visa on arrival that lets them do normal business travel things. They just can't take a local job.

To the upthread comment, neither myself nor anyone I know has ever been aware of any particular tax implications associated with ordinary business travel.