why is a 13" tonearm design really superior?

we just mounted the SAEC WE-8000 on my Nakamichi and I can´t really believe what kind of fantastic sound this tonearm is able to reproduce. Is it because this is a very special 13" design or because of the extraordinary headshell design? I think it is the only tonearm with such a long straight alu-pipe. Am i right? Also the lift design is unique, this lift stops at every level you like to use.
Why are todays tonearm developers not anymore going for a 13" or 14" design?