There are a lot of reasons why players do not come in to the net these days, including the speed of the shots and the technology that has enabled the top pros, and recreational players, to hit incredible spin with a lot of pace.
But lastly and probably most importantly, is the fact that most coaches over the past 20 years have fallen in love with the baseline game. Because of the emphasis on baseline play, we have not spent enough time working on the fundamentals of a good volley. The basic idea on the volley should be to use as little racquet movement as possible and to hit the ball in the center of the racquet. This sounds easy but because the game has shifted to a mostly power-oriented style of play, players tend to overhit their volleys by attempting to add pace to the shot, regardless of the speed that the opponent just hit the ball. This results in a lot of racquet movement, a lot of miss-hits, and very often a passing shot that the volleyer is unable to touch.
I would recommend trying to practice your volley against a wall and focus just on minimal racquet movement and a solid hit. Keep expecting the ball to come back-the wall never misses. Once you feel good about the wall practice, get a player (or your coach) who is a good volleyer, to hit reflex volleys back and forth from a position close to the net. Expand on this idea and hit one shot each trying to allow your opponent to hit it back and then try to win the point.
Finally, try to challenge yourself to go into the net during an actual point. Roger Federer says, "I know you can easily get sucked into that mode when you don’t want to attack, but if you can’t volley you aren’t going to go to the net."
Practice your volleys, spend more time up there in a match and when working on your game. Remind yourself of Craig O'Shannessy's (strategist for Novak Djokovic) statement, "The net worked yesterday. It works today. It will work tomorrow as well."