Because the security and comfort of being fed and taken care of are worth much more to them than the risk associated with living a free and wild life.
Why do some people willingly choose a life of following directions instead of giving directions?
Because the promise of "do what we say and we'll make you rich, successful, and happy" was a really tempting deal that industrial society created. In exchange generations of people gave up the freedom to live a more meaningful life to the fullest because it involved the risk of making decisions and mistakes.
But now, when the industrial age is fading away, it's safer than ever to do something that matters regardless if you're doing it alone, with the resources of others, or within the existing organisations. Today we don't reward people who just try to fit in more. Instead, we cannot help but be in awe of people who are comfortable with the risk of standing out.
The doors of the cage are open. Will the bird fly out?