This is the problem with many of them:
"Total market index funds are typically “cap-weighted”. In English, that means that most of your money, when invested, goes into the largest companies based on market capitalization.
So if I buy a mutual fund investing in the entire US stock market I might own over 3,000 stocks, but most of the money I invested goes to buying companies like Apple, Exxon, GE, Chevron, IBM and other massive US firms.
That may sound good to some investors. “Great, I own the most successful US companies. Now I can sleep easily.” Here’s the problem.
Concentrating too much money in ANY one area of the market can lead to less than desirable results over long periods of time. Case in point: From 1966 through 1982, the S&P 500 (another popular cap-weighted index) had an annualized return of 0% per year when inflation is considered. From 2000 through 2012, the index lost .7% per year to inflation. Those are long stretches of time to go without returns, especially if you depend on your investments for income.
What is important to understand is that different areas of the market, which are not well represented by these funds, did quite well during these periods in history. Smaller companies, which only make up a tiny fraction of the holdings of total market funds, can be the real game saver when large stocks go through their periodic seasons of draught. We also need to recognize, as investors, that the biggest and most important companies of today will likely become the “has-beens” of tomorrow due to changes in technology and competition. "
SOURCE:
An Easier Way To Invest? ? Paul Winkler, Inc