[DaiPlusPlus]

I speculate they needed a DRM-capable container in case the rightsholders demanded DRM when iTunes started selling lossless audio files.

[savoytruffle]

ALAC did show up at the same time as the first AirPort Express in 2004, and it is the format used to transport audio over AirPlay (first called AirTunes). That may have been the original impetus.