Over all of history, there is no accounting for what "the mainstream" decides to believe and do. Many people (wrongly) think that "Darwinian processes" optimize, but any biologist will point out that they only "tend to fit to the environment". So if your environment is weak or uninteresting ...
This also obtains for "thinking" and it took a long time for humans to even imagine thinking processes that could be stronger than cultural ones.
We've only had them for a few hundred years (with a few interesting blips in the past), and they are most definitely not "mainstream".
Good ideas usually take a while to have and to develop -- so the when the mainstream has a big enough disaster to make it think about change rather than more epicycles, it will still not allocate enough time for a really good change.
At Parc, the inventions that made it out pretty unscathed were the ones for which there was really no alternative and/or no one was already doing: Ethernet, GUI, parts of the Internet, Laser Printer, etc.
The programming ideas on the other hand were -- I'll claim -- quite a bit better, but (a) most people thought they already knew how to program and (b) Intel, Motorola thought they already knew how to design CPUs, and were not interested in making the 16 bit microcoded processors that would allow the much higher level languages at Parc to run well in the 80s.