Destiny has only sold around 11 million copies respectable but far short of the 25 million Activision claims. The 25 million is unique accounts that have played destiny so anyone who played the demo, barrowed the copy of a freind, bought one used, whatever counts toward that. But bottom line that's how many copies of the game are out there obviously not all those who bought destiny are currently playing. I'd say it's pretty obvious the player base is declining just because of how long it takes to match make or find a raid group.