Case-sensitivity is, more or less, a default: you have different strings that have distinct encodings, so you treat them as different identifiers.

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.