The alternative to case-sensitivity requires your compiler to know about case, and, more importantly, how to do case-folding. At that point, you can either choose to (a) restrict identifiers to a Some (probably ASCII) limited subset of characters, (b) only make some subset of acceptable characters (reliably) case-insensitive, (c) require every compiler to have tables for case-folding.

That's before we get into the locale-dependence of case-folding, which makes the letter "i" unreliable.

And you still have to distinguish Color and Colour.

If I define a variable as "groß", does "GROSS" or "GROẞ" match it (or both, which probably implies "gross" would match as well)? What about "ê" and "E"? Or the infamous i/I/İ/ı debacle, which could make matching "insane" to "INSANE" locale-dependent? How do you define case-insensitivity in a way that makes sense?