Check out perlop Auto-increment and Auto-decrement for an explanation.

The thing to consider here is that the .. range operator leverages the semantics provided by ++ (auto-increment). The documentation for auto-increment says this:

The auto-increment operator has a little extra builtin magic to it. If you increment a variable that is numeric, or that has ever been used in a numeric context, you get a normal increment. If, however, the variable has been used in only string contexts since it was set, and has a value that is not the empty string and matches the pattern /^a-zA-Z*0-9*\z/ , the increment is done as a string, preserving each character within its range, with carry:

    print ++($foo = "99");    # prints "100"
    print ++($foo = "a0");    # prints "a1"
    print ++($foo = "Az");    # prints "Ba"
    print ++($foo = "zz");    # prints "aaa"
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The components of the range you are trying to construct do not meet the criteria for Perl's built-in autoincrement behavior.

However, if you're using Perl 5.26 or newer, and enable unicode_strings you can use the following, as documented in perlop Range Operators.

   use charnames "greek";
   my @greek_small =  map { chr }
                          (ord("\N{alpha}") .. ord("\N{omega}"));
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Or forgo the \N{charname} lookups and just use the actual ordinal values:

   my @chars = map {chr} $ord_first .. $ord_last;
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