There really is no good slots right now and no horror movie opens in October anymore. Late-August or Early September are when they tend to open so they can maximize profits throughout the season. Releasing at the beginning of October would end up competing with 20th Century's Death On The Nile.
August is jam-packed and, but WW1984 should have petered out by then. Honestly, if I was Disney, I would've pushed up the opening to August 21st. There's a lot of smaller films that weekend, but The New Mutants would be the bigger name. Then the 28th would have no real new competition and September 4th is when you run into A Quiet Place.
Simply put, the release schedule is jam-packed right now. You have to take what you can get.