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 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.
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.
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.