Professionals do it for a living and get paid to win.
Amatures I can believe do it for the fun of it.

They play to win, even of it’s just a hobby.

If a professional athlete doesn’t win, they’re not going to be chosen for teams and they’re not going to be getting big payouts (from golf tournaments, tennis tournaments, etc.). Hopefully they enjoy the sport they play, since they would be practicing it many hours a day, most of the year.

The question sets up a false dichotomy.

It is not uncommon for retiring pro athletes to say, “it wasn’t fun anymore”. While winning is more fun than losing, many athletes enjoy the physical activity and the competition even if they don’t win.

They play to win money. And it’s easier than actually working.

They got that good by being very competitive.

I played volleyball whenever I could. On one church group (People not known for athletic ability) I busted my ass every game. One woman came to me confused.
“Why do you play so hard? We’re just here to have fun!”
I said “Playing hard IS fun to me.”
She was left confused.

I think it depend on on each person.
I for one did not put in the same “game” effort during “fun” games.

There is a difference between scrimmages and games for fun. Scrimmages were a sort of practice game but a score was still kept.
Fun games are supposed to be just that. Even if you kept score, the focus was on having a good time.