Became billioniares through having most of their assets in index funds.
That's the same question you asked 5 comments upthread from this one. Apparently you found my answer unsatisfactory since you just asked (what I now understand to be) the exact same question again, but unless you care to indicate what was unsatisfactory about it I'm not sure what to say that I haven't already.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
Notes for future OT posters:
1. Please add the 'open_thread' tag.
2. Check if there is an active Open Thread before posting a new one. (Immediately before; refresh the list-of-threads page before posting.)
3. Open Threads should be posted in Discussion, and not Main.
4. Open Threads should start on Monday, and end on Sunday.