Why is “Buy and Hold” still an effective investment strategy?

In professional funds, effective trading strategies are generally kept secret to avoid them getting “crowded out”. Each strategy tends to have a maximum amount of profit it can generate, and the more people that use the strategy, the less profit that strategy returns. Buy and hold, on the other hand, seems to have no such restriction. Even though it is one of the most well known and commonly executed investment strategies, it's still very effective. So effective, in fact, that it outperforms the majority of active investment strategies as well! So what makes “buy and hold” one of the most effective investment strategies, even though it's one of the most common?