You get disconnected in Single Player games as you can easily exploit the game and there is unnecessary load on the servers.
There was this exploit where you open an Act 2 game and go near one of those (green, blue, red) obelisks that spawn spiders on a regular basis. With enough armor, health regeneration and damage on hit you could kill them by just standing there. They drop some gold, so you could easily do this all day and collect the money from time to time. I bet there are many similar spots throughout the game.
In Multiplayer games it is different. The monsters get more difficult, so no one will accept someone just standing there doing nothing, as they have to do more to get the same amount of loot. At least I would leave and create my own Singleplayer game.