intriguing rumor was that they were designing a Marvel roller-coaster to be built over the top of the sleepy corner of Hollywood-land where the Monsters Inc. ride is. What I've read is that Chapek simply became impatient with the process and decided they needed a Marvel thrill ride ASAP, he pointed his finger at Tower of Terror, and despite everyone else's advice to leave it alone, he ordered them to proceed. Now Chapek is Public Enemy #1 of all the Disneyland aficionados and bloggers.
Chapek comes from a commercialization and revenue-generation background, so from his point-of-view, it's not hard to see how a Guardians of the Galaxy ride would drive more sales-revenue than a ride dedicated to the old Twilight Zone shows.