[ronaldx]

We might consider that the existing, originally successful designs are products of competition and natural selection of early alternatives, both within and outside of the company. In other words, it's plausible that good design is evolutionary. The rest of my comment explores this idea.

If so, these existing designs are really the best-of-the-bunch, beating out the competition, and perhaps this is because they are better on criteria that have been overlooked or not fully understood.

Now that Facebook, Google, Wikipedia have "won" the competitions in their original space, we might believe they are no longer under strong selective pressure of competitive evolution.

Facebook and Google might therefore be inclined towards major redesign which benefit them more for commercial reasons. This alienates some people, yes, but since the companies no longer have to fear immediate challenges from competitors, they can afford to provide users with a less optimised and more profitable design.

Wikipedia has no real motivation to change the design away from one which is known to be good: nobody strongly benefits from a major redesign.