In Brazil it's definitively a group thing, specially families. Friday night is pizza night in a lot of homes. I left Brazil 7 years ago so maybe some things have changed, but never once I have ordered a "smaller" pizza for personal consumption. They do exist here in the US, in some restaurants, or even takeout, so I suppose some people order them here.

Here (in TW), not only is a pizza a group food, but it's just a component in a meal with other group foods like chicken, fried potato balls, sausages, or noodles, etc.

In fact, US pizza chains struggled here until they started localizing and adding more foods to their menus!