I personally think they should have created a new game and kept this cash cow as it is. Some of us liked the 2D as it was nostalgic and similar to what we played growing up. Every football manager game out there is 3D, where is the differentiation? I am sure they will make more, they would have made more creating a new game as well. This is probably just less work for employees.
Anyway hopefully all players playing on old devices are willing to upgrade. They will definitely get more players with 3D. Hopefully retention of existing players doesn't fall short