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The reason is very simple. There was a big picture motivation: the war, followed by the cold war. Once the big picture motivation wasn't there anymore, that sort of organizational structure(or lack of it) does not work the same way. What ends up happening is what a sibling comment has noted:
> My observation has been that smart people don't want this anymore, at least not within the context of an organization. If you give your employees this freedom, many will take advantage of it and do nothing.
</paraphrase>
You might say, but `grep` wasn't used for war! Correct, but it came up as a side effect of working on much larger endeavours that tied into that bigger picture.
This has been true for most of recent human history. You might know this already, but Fourier was part of most of Napoleon's expeditions, and his work on decomposing waveforms arose out of his work on the "big picture": ballistics.