What we are missing in this discussion is that skaters don't perform jumps with no preparation for all the obvious reasons. They first do some progressives and/or crossovers to build enough speed. Then the slowly do the two three-turns in and then plant the jump. Most skaters telegraph their jumps to a smaller or larger extent. If you do a 3toe/3toe combination, everything that I've written above goes away. You have to perform a 3toe right off the landing of a triple toe. Unless your first 3toe was perfect you won't have ideal balance or landing speed, you'll be fatigued because of just having landed a jump and even if that landing was perfect you have to perform a triple jump with no preparation. Also, you can tack a 2toe at the end of the 3lutz even if it wasn't landed well. You cannot tack a 3toe at the end of a 3toe if it wasn't landed well. Unless you're Stefan Lindemann. The overwhelming amount of ladies aren't doing 3toe/3toe now. If you look at the jump progression of skaters as they go from junior to senior, in the vast majority of cases they first perform 3lutz/2toe before being able to perform any 3/3 combos. Hanyu had a consistent 3axel before he was able to land any 3/3 combos. The answer: The gain not worth the effort put in. Working on 3lutz/3toe or 3flip/3toe makes much more sense because in an ideal world you want to do both 3flip and 3lutz in your SP.