This is really correct behavior, actually. Most users will wait for a menu to load before doing anything.
But if you really want to prevent the viewer from speedily bypassing the menu, then turn off all user operations on the menu (and maybe the disc itself). Or create an empty timeline which has an end action set to the menu, and set it to the Main Timeline.
Joe, great stuff! I’ll check it out. Both my wife and sister immediately hit the play button and never knew about the menu.