Just a complete random guess... but I would expect them to have events mapped out so players can earn maybe 80-100K frags over the course of the event, allowing them to get 4 or 5 of the 6 Odins (120k frags needed for all of them).. and NOTHING else. So that way.. purchase is required if you want all 6 Odins and things like the Freya cosmic, etc along the way. This would be "true to form" for most events.