A stockbroker trading in the markets is akin to a real estate broker buying and selling properties on his own account. The argument you are making is that the real estate broker will know which localities will demand a premium property rate in the future based on the transactions his clients have made. The real estate broker might be in a position to make better decisions because he has seen more properties but his decisions need not always make him a profit. Further, the transactions of the real estate broker’s clients have little bearing on how he views the property markets. Similarly, a stockbroker when trading on the stockmarkets is influenced by his views on the market. A stockbroker will not be able to foresee which client will make money in the future or which ones won’t. So, instead of betting on a clients position to go in either direction he would rather focus his judgement on the markets as his clients would too. If you had access to all your friends trades for the next year, who would you copy? It isn’t guaranteed that the ones who made money in the past will make money in the next year.