I think it's largely a feeling of "what will they remove next"? Say an engineer is a a daily user of ten particular GNOME 2 features. GNOME 3 removes four of t

I think it's largely a feeling of "what will they remove next"? Say an engineer is a a daily user of ten particular GNOME 2 features. GNOME 3 removes four of them, and hides three more. At that point, the engineer is wondering what will happen to the rest when GNOME 3.3 comes out. In contrast, environments which are explicitly intended to be customised very rarely disable or remove features. Someone who's been using the same configuration for ten years can know that if it works in release N, it'll probably work (maybe with a few minor tweaks) in release N+1. It's worth noting that XMonad has many more features than Metacity; it's not bare-bones by any means. Converting to it isn't like converting to a minimalist WM.