Why do soccer-football managers stand right on the sidelines?

You often see the managers of these teams standing (and when their side is losing) yelling on the sidelines. This is not the same for other sports such as tennis, cricket, swimming, track etc. Don't they have a trainer to relay tactical messages to (from a corporate or team box)? Why is the standing and yelling necessary for their role? Is it all about 'making an appearance' to promote themselves as more pionate in the public eye (to be seen as a involved spectator rather than aloof manager)?