It's REALLY simple: Marvel Studios has the strongest franchise track record in the business right now. Fox doesn't. There's nothing "straw man" about that. Even Marvel's "lesser" movies, barring The Incredible Hulk when they were first establishing themselves, were hits. Changing decisions about movies before they're ever made is one thing; delaying movies that have already been shot or are currently in production is a whole other can of worms. Fox X-Men movies have been the most hit-or-miss ongoing franchise around. They don't have the track record to back up that kind of confidence when one of their productions is seemingly trouble, especially when they've just lost the rights to the IP and have even less incentive to ensure a quality product for the longevity of the brand.
Captain Marvel has run as smoothly as any typical Marvel production, so they've given us no reasons to doubt it.