They want to get their return as fast as possible. There’s no major benefit to waiting a year to put it on Disney+ when they could possibly be getting *some* streaming in the meantime. It’ll be just as big next October whether it’s brand new on the platform or not.
Unless it absolutely tanks in theaters and gets immediately sent to Disney+ like Encanto did (Which proved popular with families once it was very easily accessible, but probably won’t be repeated here), they want a healthy window between the film’s release and its arrival online. Opening in July gives them a couple months of buffer before it hits Disney+ at . . . I’d guess the end of September/early October.
They want enough time to try and discourage people from waiting who might otherwise see it in theaters, but also not SO much time that people forget it even existed. Disney+ (among other streamers) think they have a problem with dead media taking up space but getting no viewership. This will probably not be one of those, but waiting a year and letting people forget the thing exists - especially if the box office is soft - wouldn’t help.
They seem to think this is their best shot with Haunted Mansion.