Because what we call "lemonade" in Europe is not the same drink as what is called "lemonade" in the US, although we usually have our own variation (citronnade in France) that corresponds to the American one.
Where did this bullshit come from? Sprite is not lemonade in Europe or Australia, it's lemon and lime and I don't know anyone who doesn't know that.
There's loads of brands of lemonade here and Australia, cloudy, traditional, clear...wtf?
Wikipedia saying " In the United Kingdom, Ireland, Central Europe, South Africa, Australia, and New Zealand, a carbonated lemonade soft drink is more common. Despite the differences between the drinks, each is known simply as "lemonade" in countries where it is dominant."
Quora saying “Lemonade” in Australia normally refers to a clear, carbonated, lemon-flavored beverage similar to 7-Up. “Lemon squash” is a cloudy version of the same thing (still carbonated). There’s no particular tradition of making non-carbonated lemon drinks at home, but if you did, you’d probably call it American-style lemonade."
I see on the Wikipedia article it seems to say that lemonade in the USA is flat, not fizzy? I think this is where I confused your question and we got our wires crossed. Anything that ended "ade" in the UK is a fizzy drink, like a pop/soda. Lemonade, cherryade, orangeade etc. Schweppes, Barr's etc make lemonade like that, clear, sweet fizzy and just lemon flavour.
I can't think of a drink that's fresh lemon juice as described on wiki over here. There is squash, or cordial, diluted juice with water. But lemon wasn't common or popular to the best of my knowledge. I'll look when I'm in asda the morn now though, just to see for curiosity.