I totally agree with you but OP asked about how things are, not about how things should be. https://example.com/{en,fr}/page.html https://example.com/{en,fr}/p

I totally agree with you but OP asked about how things are, not about how things should be. https://example.com/{en,fr}/page.html https://example.com/{en,fr}/page.html is indeed much better—and widely recommended, for that matter—but lots and lots of sites don't do that for one reason or another. If those sites use a cookie to store language choice, then it is IMO quite reasonable for the site operator to consider such a cookie as "required".