High school baseball is expensive. Between the participation fees and the mandatory booster club costs, ads and other miscellaneous costs, it adds up over 4 years. All that for a 20-25 game season.
As for the decline in attending games, the reason is baseball plays weekdays at 3:30-4:00PM start times. Most peeps work that time and with both parents working hese days, they don't get to see any games.
I would have liked 7:00PM starts. Wouldn't have missed so many of son's high school games.
If games started later, parents could make games and more of the locals might come out to a high school baseball game but since they start during school hours and play into rush hour, peeps aren't gonna catch games and certainly aren't gonna take off from work to watch a game.
If baseball could be played under lights and start at 6-7PM like football or basketball, you would get more support at the games but those start times are unlikely to ever happen since most high school fields have no lights and with school budgets and putting most of the money in athletics into the football programs, baseball fields won't be getting lights for night games.