There many reasons and most have been posted imo. But there are more. When I first started coaching in hs I wanted to give my hs players a baseball option in the summer after the hs season ended. We had a legion program that was 25 miles away and our kids usually were not selected to play. Only the top one or two guys ever made the team. So I put together a summer team comprised of all our returning players and the rising 9th graders that wanted to play. By the 7th or 8th game of the summer season I was having a hard time fielding a team. Beach trips , trips to the lake , softball , etc etc.
One of the problems is when kids reach an age where they can decide if they want to play or not , girls , cars , hanging out with friends , etc etc they make the decision that its just not as much fun to them. If you add in the fact that you actually require them to work at it. You actually demand that they bring it everyday and compete they fade away. This is not only a problem in my area but in many areas. You can give kids the same opportunities that many of our sons have. Travel every weekend to play baseball , work out everyday to get better etc etc. The fact is very few love the game enough to want to do it. Very few are willing to work to reach the level that others are willing to work. Oh yeah they like to play. But after awhile they are ready to move on to something else. And they like to play but they dont like to work at it.
When you start demanding that they actually invest into something the numbers start to dwindle. They will always dwindle. Because the fact is alot of kids want to be players. Very few are willing to do what it takes to be a player. There are alot more things for kids to do today. There alot more distractions. Select teams and travel teams have players on them that play almost every weekend and work out almost everyday. Why? Because they love it.
Open up the field and offer bp to anyone that wants to come. Who shows up? The kids that worked out all day already and played games all weekend. Where are the other kids? The parents of these kids are the first ones to complain about their sons playing time. The first ones to complain about pratice lasting too long. The first ones to complain that their son didnt make all conference. The ones that complain that the coach doesnt work hard enough for his players.
The fact is the kids that love the game and want to play the game are going to. They dont have any problem finding the time and giving the effort at the other things they love to do. When kids reach hs its not LL or pony league anymore. You have to invest in your game and your program. The fact is most do not want to. So they move on to other things. It has nothing to do with the kids that love the game. It has everything to do with the fact that some simply dont. And when the effort it takes to be a part of something is too much for them they move on to other things.