Off sites are a great way for team members to get to know each other on a personal level. With stronger relationships, people are willing to work harder for one another and are better able to find common ground when conflict arises.
While managers know the value of these events, they are often left unscheduled because they're labor intensive to plan. Not only do managers need to find a good time, but they also need to think of an enjoyable activity.
I suspect many managers would be willing to pay to have someone else take care of the logistics of planning novel team outings that people would be excited to participate in on a regular basis. Ideally, this would include a menu of potential events; and once one is selected, everything would be arranged without the need for further input.