I always imagined he was perfectly willing, but John was so deep in denial about looking like a true and authentic woman and not a snarling ogre that he was too stubborn to ask for it. It's the same reason he never updated his wardrobe, I don't think Frank was forcing him to wear that one black dress over and over. Obviously, John will always have a hard time shopping for actual women's clothing, but with Frank's wallet at his disposal, I'm sure he had plenty of options for getting things tailored. John was more focused on important hobbies, like buying pinball machines he barely uses, cars he never drives and the latest Apple product to check Twitter, so he never bothered with things like fashion or applying makeup. If I had to guess, it only became an interest when John started making friends with Keffals and other troons and they'd shit talk all the other troons for failing to pass.