If I am going to believe random articles I found on the internet (and, of course, I am), the reason is because SQL was originally called SEQUEL until the creators ran into a trademark issue.. They changed it to SQL, but us old timers just kept calling it the old thing. Something about old dogs and new tricks.
https://medium.com/tableplus/how-to-pronounce-sql-properly-s-q-l-or-sequel-7203a5185676