So who became Xerox? (i.e., brilliant ideas, thrown away at the corporate level)

Xerox was a weird mix. Insightful enough to fund PARC, but blind enough to not understand the computer market. There's a section in "Fumbling the Future" describing how Xerox higher-ups could not figure out why people thought the Alto, with it's bit-mapped / mouse-based interface was in any way different from SDS/XDS minis with a set of front panel switches and serial terminals hanging off the back.

MSFT maintains a research arm (MSR) which routinely produces interesting concepts. Not that they would ever try to turn them into products. So maybe MSFT also turned into Xerox.

They died of Fatal Neglect because no one gives a shit about brilliant ideas anymore.