ATRAC was just to avoid the onerous MP3 license fees, AND lock-in consumers.

Sony is all about NIH. They never release a product unless it uses their own proprietary something-or-other. Remember memory stick? Hi8? UMD? PS Vita memory cards? MicroMV? MiniDisc? HiFD drives? SuperAIT? AVCHD? Why do you think DAT didn't use some other existing tape format like Digital8?