It might be due to the fact that CAPTAIN AMERICA: CIVIL WAR is currently in production and there's nothing to show in time for the 2015 San Diego Comic-Con International — which is actually a crap excuse since GUARDIANS OF THE GALAXY footage was shown just 12 days after it started filming and Civil War has been filming for well over a month now. Or it's because Disney's D23 Expo is the month after. But, per Deadline, Marvel Studios will not attend SDCC next month.
This has been the rumor for several months and quite honestly (in my opinion) it's probably because of D23. However, Deadline does claim that Marvel Studios' president Kevin Feige doesn't have anything cool to show the fans in Hall H of the San Diego Convention Center.
This isn't the first time the studio has passed up SDCC because they did it in 2011, too. So there's no need to freakout about this. Unless the whole reason you were planning to go to SDCC and paid the expensive cost for tickets, hotel, airfare, etc. was to see the Marvel Studios panel. In this case, you're definitely allowed to freakout.
It is widely assumed Warner Bros. will take over the closing panel time slot now vacated by Marvel Studios on Saturday night to reveal a ton of things for BATMAN V. SUPERMAN: DAWN OF JUSTICE, SUICIDE SQUAD, WONDER WOMAN and maybe even AQUAMAN. This year is Warner's to shine at SDCC because they are without their biggest studio competition.
Marvel Studios' Hall H presentation has been the big panel to attend every year at Comic-Con since 2009. Fans will literally camp out in line the night before and stay in line through Saturday until the evening when the Hall H doors open for Marvel Studios.
Meanwhile, D23 is in August and Disney has already confirmed both Marvel and Star Wars will have a large presence and presentation on Saturday of that event.
Marvel Entertainment will still have as large of a presence as they have each year at SDCC with their large showroom booth as well as with their comics, video games, merchandise panels and more. Just the studio is sitting out the annual pop culture extravaganza.
Related Post: Marvel Will Have a Booth at the 2015 San Diego Comic-Con but Marvel Studios Might Not be in Hall H