org-sort has an optional argument with-case. By default its sorting ignores the case. When org-sort is called within a table, it calls org-table-sort-line with the argument. org-table-sort-line defines a let variable sort-fold-case (not with-case) but fails to use either variable when sorting and always sorts with case.
This is with the very latest org:
Org mode version 9.1.13 (9.1.13-elpa @ /Users/helehvas/.emacs.d/elpa/org-20180702/)