At the end of the day it's all about probabilities.
Let me tell you something - learning to fly is "risky"! Now I know we are not allowed to use that word but it's true. Of course as instructors we are doing everything we reasonably can to eliminate the risk. On early solos the instructor is making most of the "command" decisions, e.g. weather, atc situation, student skill level, etc.
We could perhaps teach them everything in the syllabus before they go solo but we don't - what about Steep Turns just in case he has to take emergency avoiding action on his first solo - ever seen a bandit flog straight through the ATZ without clearance? But this just would not be practical. We have to be careful we do not generate a problem by fixing another one.
The basics of learning to fly are very simple and it's plain counter-productive if you start to complicate it in the early days of the students flying.