Golden advice, Knights.
IMO, age group has nothing to do with it. However, HARD WORK has EVERYTHING to do with it. It's not that the hitting is getting worse, it's usually a case of hitting skills not keeping up with all the other skills. Hitting, like pitching, takes a lot of time to master. As kids get older, we ALL know about the other "interests" that sometimes steal the focus from softball - just at the time when they should be working very hard - IF they want to extend their play to the college level. Granted, that's simply not for every kid. Recreational level suits a lot of families just fine.
Along about 14u - 16u, priorities for kids start to become a little more focused, and sometimes take the unexpected fork in the road. So, I wouldn't blame a team coach at all. As a matter of fact, I RARELY blame a coach for the kids performance and skill level. I put the responsiblilty for skill improvement squarely on the shoulders of the player. "Ask NOT what your team can do for you, but rather ask what YOU can do for your team!"