This is true in hindsight and seemed obvious at the time, but in fact Apple insisted that Carbon was a long-term solution and treated it as an open-ended commitment. They dogfooded it internally, using it to write the Finder and iTunes, two first-party apps so central to the user experience that novices confused them for the OS itself. There were working betas of Carbon 64, and Apple's decision to reverse course and deprecate Carbon on 64-bit platforms in the middle of the release cycle caused significant developer whiplash.
Nobody with any sense really believed Apples protestations during the 1999-2007 time period that Carbon was going to be a long term solution, but Apple really tried to sell folks on the idea that it would be, until they suddenly low-key ghosted on the Carbon developer community at WWDC 2007, when 64-bit Carbon was quietly removed from the keynote deck a year after it had been prominently featured.
Apple didn't present Carbon as merely a compatibility layer at the time. It was positioned as the procedural C paradigm alongside Cocoa's and Java's object-oriented paradigms. Carbon was supposed to be one of the three development frameworks for OS X alongside Cocoa and Java, which is why Cocoa and Carbon have drink-themed names to fit with Java. Porting a classic app to Carbon was "Carbonization."
