No they don't automagically make every single person happier, but breaking up monotony, providing at least neutral distraction, and opening up the door to directly interesting activity all can have a huge impact on someones' happiness. Even getting healthier with exercise does help ... eventually, if you stick with it and don't despise the activity.

Just because they're not a silver bullet shouldn't reflect too poorly on the general advice. Though it IS important to remember that many peoples' sadness absolutely cannot be solved so simply, and giving basic advice for troubling problems can be down right insulting.

The point of general advice is not to make people happy, but to open the door to enjoyable experiences that can. Analyzing them as direct happiness is of course far, far too subjective. Analyzing them as direct sources of happiness kinda'... misses the entire point on why these activities are so commonly recommended.