Their most recent World Series wins were in 2009 (21st Century/3rd Millennium) and before that in 2000 (20th Century/2nd Millennium).
Remember, there was no year 0.
And any cutoff point is convenient based on the argument being made. In my lifetime, dating back to 1985, sure the standard for success is different as well. But twenty years is a pretty hefty recent standard in the realm of pro sports, and it fits neatly with a pretty universal time barrier.
Heck, if a time traveller told us that our favorite team was twenty years away from their next title, we'd all be bummed out at such a long wait even recognizing that longer and actual droughts are a thing.