Franchise fatigue definitely in COD and Halo. They've been around a long time, changed developers, and haven't innovated enough or brought enough 'new' things to the table past their break out games.
Battlefield 1, given it's only a 2016 title, both titles still in the top 40 per week and given digital is anywhere from 20-30%, it could even outperform Battlefield 3. Battlefield 4 is a cross gen title landing in 2013, you have to consider the timing, the sales base was split almost evenly between this gen and last gen. I think the graph needs to be longer to establish any meaningful results for this franchise.
With just a cursory look at the numbers though, it would appear as though the FPS genre is seeing a much bigger decline in NA than in Europe. It would be very interesting to see a comparison graph for these franchises growth or contraction in NA and in Europe.
In fact COD:BO3 (PS4) is the highest selling FPS in Europe. Ever.
I'm starting to think there's a correltation to console sales, but I'll need to have a closer look.
