One reason, I believe the summer box offices doesn't do well anymore, their so many damn movies trying to compete against each other. So these supposly to be be good box office movies air in the summer, which usually suck now and the really good summer movies move into the dead months now. Usually around the holiday season and beginning of the year are the new summer months.
Like for an example for the rest of 2017, some of these would have been great summer movies. But I believe this movies will probably be competing for #1.
It - Sept 8th
Mother! - Sept 15th
Kingsman 2 - Sept 22nd
Blade Runner 2049 - Oct 6th
Geostorm - Oct 2oth - I believe this movie will suck?
Jigsaw - Oct 27th
A Bad Moms Christmas - Nov 3rd
Thor: Ragnarok - Nov 3rd
Daddy's Home 2 - Nov 10th
Murder on the Orient Express - Nov 10th
Justice League - Nov 17th
Star Wars 8 - Dec 15th
Jumanji - Dec 20th
The Great Showman - Dec 25th
Early 2018
Black Panther
Pacific Rim 2
X-Men: New Mutants
But the one movie that real probably dominate all of summer 2018 is Avengers: Infinity War, maybe next to Deadpool 2, Han Solo and Jurassic Word 2.