I have seen people re-write large chunks of functionality not knowing it was already there in a form they didnt know about. Have done it myself a few times. Write largish blob of code. Replace it with one system call that does the same thing.
Also most things are simple. It is the data and libraries and applications from those simple things that are interesting. Take for example C++. The actual language is a few dozen keywords. But the libraries and things built using those small things is quite large.
Also most drivers are written so that we can re-use the code. But with the right docs you can twiddle the hardware yourself. That was 'the 80s/90s way'. It was not until macos/os2/windows/xlib that we abstracted the hardware. Mostly so we could consistently reuse things.
Also most things are simple. It is the data and libraries and applications from those simple things that are interesting. Take for example C++. The actual language is a few dozen keywords. But the libraries and things built using those small things is quite large.
Also most drivers are written so that we can re-use the code. But with the right docs you can twiddle the hardware yourself. That was 'the 80s/90s way'. It was not until macos/os2/windows/xlib that we abstracted the hardware. Mostly so we could consistently reuse things.