For a big conference, one that attendees spend lots and lots of money to travel to and attend, the pressure on the organizers is to make sure that all the prese

For a big conference, one that attendees spend lots and lots of money to travel to and attend, the pressure on the organizers is to make sure that all the presentations (and presenters) are at some baseline level of quality so that attendees will go away happy. They are much less concerned with providing opportunities and teaching moments to aspiring conference speakers, which hopefully everyone agrees is the right set of priorities for an organizer for that type of conference. There are all sorts of ways an aspiring presenter can get experience or demonstrate ability that don't involve catching a break from a sympathetic organizer whose job is looking out for the attendees that spent thousands of dollars to be there.