I buy every book on release, not only as a GM looking for more game options/rule, but also as a fan of both the license and the RPG FFG have created. With my group of friends, we have been playing since the EotE beginner game was released. When the EotE rulebook came out, only one out of a group of 5 picked up one as well.
When Enter the Unknown was first announced, I realised that I didn't want everyone at the table relying on me to buy every single one of the books to then bring with me week after week. I quickly discussed with my friends that I didn't want to bring everything with me week after week. Not only that, I was also concerned that game play would slow down with everyone passing around a single copy of each book (similar to how we shared the Core Rulebooks for the first few months) looking for one little thing.
The solution was an amicable one, similar to what happened with my previous Pathfinder groups. If a player wanted the goodies found within a Career Sourcebook (minus species, which everyone has access to everything when creating a character) then that player should have their own copy of it. That way, players could plan advancements at home, learn more about their career, not rely entirely on me and support the game with a single purchase.
Thankfully this worked out really well and everyone at my table has ended up buying at least 3 of the 5 career books up until now to get access to the different tech and skill trees. For this group it was a fair deal and they all ended up buying a copy of Lords of Nal Hutta upon release based on sheer love of the Hutts alone.
So they don't support the game as often as I do and only one hasn't go any of the CRB's, but they still do when something really special to them shows up.
What does everyone do with their groups? Do you share one book between many or do you have a similar rule to mine to prevent the group being entirely dependant on you? Are members of your group similar in buying one copy of everything?