Online brokerage has grown by appealing to the smallest, most aggressive, self-directed segments. There just aren't any of these people left.
If the ante is lower, then you're going to play hands you probably would not play.
Firms need to change what they're offering. Schwab is doing an excellent job of this, with the little classes they're running for folks -- this is what a P/E ratio is, this is what a limit order is.