They don't target something else because they wouldn't be an index fund, that's just a passive fund with their own published strategy. Those exist but aren't as popular, the appeal of index funds is that you're just getting "the market" and "the market" is measured by the index. Public indexes are supposed to be lower-cost and less manipulable, but that was before they got large enough to "wag the dog," which is the ultimate point of the article.

Because when I buy QQQ expect it to track the Nasdaq-100, not something else.

Vast majority of index funds do not track NASDAQ 100.