Commuter rail in the United States mostly caters to affluent suburbanites who commute to the city center. Even though these lines pass through working class city neighborhoods that stand to benefit enormously from better transit, the service they provide passes those communities by. It doesn't have to be that way.
In Europe it's common for regional rail systems to get ridership comparable to that of the subway in the central city. But in America, this is unheard of. One reason for the discrepancy is land use: American commuter rail stations are typically surrounded by parking, while in the Paris region you see a different pattern with ample development next to suburban train stations.