I think one reason is the senior DICE members who made older BF games have moved on to other studios (Embark Studios being one of the latest).
If it wasn't for portal I would have stopped playing long ago. CoD is matchmaking only and it killed the game for me. I'm to the point that if a game is matchmaking only I'm going to pass on it.
Portal could have been much bigger but it took way too allow full xp for anything outside of the official experiences. It still lacks in some areas but I don't think it will be updated to a point that people come back to it.
If DICE doesn't want to add the browser to AOW then add Breakthrough to portal so we can at least make our own games with the server browser there.