With respect to your why question, the funds that do well tend to:
* Have below average to lower fees (no suprise).
* Focus on asset classes where information and research can matter (like small cap, narrow international regions, specific industry, junk bonds)
* Dont churn portfolios much, generating excess costs.
* Be large enough to take advange of cost advantages from scale, but not so large that their strategy is diluted. A group like Vanguard can offer good costs by sharing resources with passive funds and limiting size of active specialized funds.
* Have a clear strategy that makes sense (e.g. Indonesian tech fund, your local researchers actually meet with and review indonesian companies management, your team closely inspect the books, clearly post in prospectus the fund is an indonesian growth stock play, move out of positions if a portfolio position is no longer attractive...but only if fundamentals changed, etc.
* Get lucky with one or more of their picks or their chosen asset class.
* Not be greedy crooks.