I agree performance is the main reason.
Another reason is that while very few people look at it, there is additional information about you GIS system stored it that you might not want to make public. For example, it may refer to another sensitive layer that was used in a clip tool. While the history doesn't provide access to that layer, it does advertise the layer's existence. In addition, full paths are often stored which gives people an idea of your network infrastructure. Most of the time, the history is garbage to start with but someone looking for info on your private GIS system could get stuff out it. Removing the history lessens this risk. This really only a concern in highly sensitive GIS systems.