I don't have the personal experience from gigs with "thousands of people", as the only ones I've been to were not that huge, and at those the merch stands were always swarmed. If you are playing for an audience that big you are probably already good on ticket sales alone (which also tend to become more expensive once a certain audience threshold is crossed).
I also wasn't just guessing/assuming that, but relaying what I've been told by friends who are musicians (see also my sibling comment).
I also wasn't just guessing/assuming that, but relaying what I've been told by friends who are musicians (see also my sibling comment).