Or in Linus Torvalds' case, laziness. He considered writing drivers and such to be drudge work, so he opened the source in the hopes that other people would do it for him.
LOL!!!!!!!!!!!!!!!!!!!!!!!!!!!!
I could go along with that.
But remember one of the UNIX sayings, "do one thing and do it well". So why not let driver writers come in and..... write drivers! lol