I'm convinced Apple has continued to "flatten" their keyboards in order to transition towards iPad-like devices replacing them entirely. For years, they've stated some variation of the following when speaking about the iPad:

"This is the clearest expression of our vision of the future of personal computing, a simple multitouch piece of glass that instantly transforms into anything you want it to be."

So in their quest to shepherd users towards this vision, they've made design concessions which have hurt their existing users.