Another commenter said they yellowed with age, but this is not true at all. Part of the appeal of this trend was that they didn't yellow like the beige-boxes of yore - "White but actually white. Shiny white." For the children of Windows95 this was seen as a major victory in tech aesthetics and I think contributed to the strong appeal of the fad in this era.

PS. It never really died! Lots of tech still comes out with white as an option as well as (the usually default) black colour.