Because the vowel sound in “lose” is more commonly spelt “oo” as in “loose”, and “lose” looks like it should rhyme with “nose” or “close” but doesn’t. And “loose” is a real world (albeit with a different meaning and pronunciation to “lose”) so people’s brains (and spell checker) don’t instinctively flag it as wrong.

Because English is not the mother tongue for the majority of the people, and correctors fix typos, but not swapped words, unless you use something like Grammarly.

Pointing out mistakes is fine, being emphatic while doing it would be great

I mostly comment on my iPad. When using an iPad it’s hard to get spelling correct. Also, language changes over time. For instance, “I could care less” is starting to mean “I couldn’t care less”. When enough people say or use a phrase incorrectly enough then it becomes the new correct way.