Spilliting a DVD can be very different from title to title. It is not easy to do it automatically and always please the user.
I usually have different "splitting methods" depending on the movie:
1.) Put the main movie completely on DVD1, put menu & extras on DVD2
2.) Put main movie & menus completely on DVD1, extras on a CD (Mini-DVD)
3.) + 4.) as 1.) and 2.), but leave out some audio tracks to make main movie fit better
5.) Split main movie, keep menus & extras on DVD1 AND DVD2, if they fit without compression
6.) Split main movie, keep menus on DVD1 AND DVD2, extras on either DVD1 or DVD2, if they don't fit
7.) as 5.), but leave out DTS track to make everything fit
8.) keep menus & extras on DVD1, put 2nd half of movie on DVD2 without menus
9.) + 10.) as 5.) and 6.), but use AnyDVD to "Jump directly to main movie" on 2nd disc
You see, it is hard for the program to decide what you want, when you say "split now!". Depending on the method used, the split point must be moved as well. If all extras are on disc 1, you probably want more of the main movie on disc 2 to avoid transcoding.
But I agree, it should be much, much easier. The current UI is not "splitting friendly", although it is not that bad, once you get used to it. Chances are good, that splitting will be improved in the future.