[gerash]

Disclaimer: I'm no historian. But my guess is it's often not a simple cause. This is a lot like how, say, tech companies evolve.

For example is there a simple answer to why, say, HP isn't considered the most successful tech companies right now while it was at some point in time?

My guess is other groups of people learn from them and surpass them overtime. This can also be true even within a single company where one org used to be the most important one but over time another org brings in more money and becomes more important