Major issue with SP games for a publisher is this. You buy the game, you buy the expansions/DLC and thats it. So lets say thats 60-80-100 bucks. Well okay then. However these publishers obviously want more money.... I mean no shit,, this is what companies want. MP games are the same as SP, you have a base game and some expansion/DLC, but now its a multi player game and thus automatically will last longer with less content. You just need some maps, some game play and thats about it, a single player game would need NPCS, writing, more mechanics, etc, etc. But since MP games last longer and have longer running audiencess, they are more likely to buy more micro transactions
Thats why we see more MP games.