Bingo. No sane investor holds QQQ because there is no academic theory behind why it should exist. Why is a stock better if it's listed on NASDAQ instead of NYSE? Can any investor answer this question? Doubt it. If you are into factor investing and you like large cap growth, you buy something like VUG. Most people should just stick with SP500 or total market.

However, QQQ had a really good last 15 years and lots of investors hold it because they are chasing returns and because the marketing worked. (The managers of QQQ are legally obligated to spend X% of the fees collected on advertising the ETF, ha ha ha.)