In a world of ASCII, maybe. But fixing one problem for a small group of people is a giant can of worms for the rest of the world. Normalization of compound characters, exotic character sets, emoji, different classes of upper/lower-case letters, normalization of compound what-not.
And even then it still doesn't fix the issue outside of the world of ASCII. A filename written in hiragana and katakana is logically the same to the end-user, but they are still distinct. Simplified and traditional Chinese, Hangul and romaja, pinyin, devanagari, thai, and the list goes on.
Case-insensitive filenames fixes nothing, but breaks everything. There is only one sensible thing to do with arbitrary user-input, and that is to leave it be.
Ensuring filenames don't get destroyed by an OS that refuses to understand a given language. Case is a complicated mess once you leave ASCII, and that's partially because ASCII is lying to you about how English case works: Yes, the English language has title case, and ASCII conflating it with upper-case does not negate that.
Move on to most anywhere else and the notion that it's fast, reliable, and safe to convert case gets lost in the realities of human writing systems.
And even then it still doesn't fix the issue outside of the world of ASCII. A filename written in hiragana and katakana is logically the same to the end-user, but they are still distinct. Simplified and traditional Chinese, Hangul and romaja, pinyin, devanagari, thai, and the list goes on.
Case-insensitive filenames fixes nothing, but breaks everything. There is only one sensible thing to do with arbitrary user-input, and that is to leave it be.