It might not be the memory concern it once was, but today it might very well be a power concern. Modern laptop display pipelines can save power if they don't have to redraw any of the screen: constantly updating status bar animations break that.[1]

1: https://developer.apple.com/videos/play/wwdc2013/712/ (I think the relatively short graphics section mentions this. Can't seem to find the talk that goes into it in more detail...)