Maemo, and its significance to Nokia, has changed significantly since the "internet tablet" days - even by the N900 time, and moreso for MeeGo.

You can imagine that the pressure and responsibility at top management is immense. I could easily imagine someone used to "easier going" of early Maemo days to want to drop out when going gets serious. In that case, nobody should feel "sorry" - the one dropping out can pursue to have some semblance of "normal life" again, and the position is filled with someone that's hungry for the new challenges.