Last but not least, some indexes (e.g. S&P 500) have recently changed requirements so that most tech IPOs (which usually have two classes of stocks, one "inside

Last but not least, some indexes (e.g. S&P 500) have recently changed requirements so that most tech IPOs (which usually have two classes of stocks, one "insider" class that has a lot of votes, and one "general" class that has few (if any) votes) would be ineligible (existing members of the index were grandfathered in).