1. The current allocation of labour isn't set in stone. Just because we have a certain number of accountants now, doesn't necessarily mean we need all those accountants for society to function in a way that makes us all happiest.
2. Almost everyone is passionate about eating and having a warm place to sleep. An accountant who quits his job to pursue a career as a rock star will likely soon run low on money, and may find renewed passion in accounting, if only as a part-time gig to feed and shelter himself and his family, while he finds greater fulfillment playing music in his spare time.
I also believe that nothing truly great gets done without there being a huge amount of passion behind it. Look at any great project you know and you'll see it there in the core people. They wouldn't want to be doing anything else. The world would be much better if everyone followed their passion. I think most of us are just too scared to let go of the security of making the safe, easy, predictable choices.