Why exactly? I'm not aware of any benefits of filenames being case-sensitive, it just opens a room for tons of very common mistakes that literally can't happen otherwise. It's not like in coding where it helps enforce the code style and thus aids readability - and even in programming it was a source of PITA to solve bugs before IDEs became smart enough to catch typos in var names. One thing I loved in Pascal the most is that it didn't care about the case, unlike the C.
The case-sensitivity algorithm needs a locale as input in order to correctly calculate the case conversion rules.
The most common example is probably that i (U+0069 LATIN SMALL LETTER I) and I (U+0049 LATIN CAPITAL LETTER I) transform into each other in most locales, but not all. In locales az and tr (the Turkic languages), i uppercases to İ (U+0130 LATIN CAPITAL LETTER I WITH DOT ABOVE), and I lowercases to ı (U+0131 LATIN SMALL LETTER DOTLESS I).
case-insensitive is all fine if you only handle text that consist of A-Za-z, but as soon as you want to write software that works for all languages it becomes a mess.
This is the main point, and almost all the other chatter is not particularly relevant. A dumb computer and a human can agree with "files are case sensitive and sometimes that's a bit weird but computers are weird sometimes". If there was indeed exactly one universal way to have case insensitivity it would be OK. Case insensitive file systems date from when there was. Everything was English and case folding in English is easy. Problem solved. But that doesn't work today. And having multiple case folding rules is essentially as unsolvable a problem as the problems that arise from case sensitivity, except they're harder for humans to understand, including programmers.
Simple and wrong is better than complicated and wrong and also the wrong is shoved under the carpet until it isn't.
Though you still ought to declare a Unicode normalization on the file system. Which would be perfectly fine if it weren't for backwards compatibility.
Except at the UI layer (where you can easily offer suggestions and do fuzzy search), the opposite is true. There are so many different ways to do case-insensitive string comparisons, and it's so easy to forget to do that in one place, that case-insensitivity just leads to ton of bugs (some of which will be security critical).
For example, did you know that Microsoft SQL Server treats the columns IS_ADMIN and is_admin as either the same or two different columns depending on the database locale (because e.g. Turkish distinguishes between i and I)? That's at least a potential security bug right there.
Why exactly? I'm not aware of any benefits of filenames being case-sensitive, it just opens a room for tons of very common mistakes that literally can't happen otherwise. It's not like in coding where it helps enforce the code style and thus aids readability - and even in programming it was a source of PITA to solve bugs before IDEs became smart enough to catch typos in var names. One thing I loved in Pascal the most is that it didn't care about the case, unlike the C.