Why does updating iTunes hide your music library?

I just updated iTunes and 'lost' my music library for the second time in a year. Interestingly, the music I had downloaded from iTunes was preserved. I followed this article (If you don't see your content after updating iTunes - Apple Support) and got it back (I also found the stuff from last year, which I had painfully reconstructed - so, I guess, thanks for that). But WHY? Is iTunes meant to be *my* tunes, or just *your* tunes? Why does a company that employs so many "geniuses" screw up so badly? Do you want me to keep using your products or start using the other guys' stuff?