Why do Americans whine and British whinge?

You left out Canadians who whinue.

The British don’t exclusively use whinge. I know I use whine sometimes. Australians use both too. I think the more common term here would be whinge but the word whine would also be used here too. I think there is a slight difference. Some people here whinge about the rules. In other words, they complain but they may do it quite stridently. If someone is whining there’s an added element of being a bit pathetic. You know like a child whining because they have to go to bed early in a crybaby way.

@Cruiser We don’t whinue, we give’r.

@dappled_leaves Thanks for setting me straight! lol. Never could quite get the hang of that apostrophe thingy with youeour’e Canucks~

@Cruiser Haha! I may have just created more problems than I solved. :/

Just different words but my theory reaches further, oh yes.
A lot of American accents sound quite nasal & whiney, so yeah, genius at work.

In New Zealand I always heard the term ‘whinging Poms’.

I would use both terms slightly differently. Whining describes the pitch and tone of voice whereas whinging describes the complaining act.

UK Scot here.