Does it truly forget? A lot of the past knowledge is locked away or it was only experienced by 1000 programmers back in the 70s. It stands to reason that the huge amounts of programmers today have to learn their own lessons.

I think maybe in 2050 or so we will reach software development maturity, once the base of experienced developers is not dwarfed by the generation of developers joining the work force in one single year.

Keep in mind that the number of programmers is not only increasing moderately in developed countries, but much more so in developing countries, where hundreds of millions of people are joining the global middle class.