In my opinion,
Most uni students have more time, thus are able to get jobs and earn money for petty things like a train ticket. Where compared to school students, they dont have much spare time in getting jobs. Also they use most of this time studying to ace the HSC LOOOL
It is also the fact that most uni students are above the age of 18, where society now considers them as adult. As for school students, theyre mostly aged below 18, where they are categorised to be a child and still under parent's guidance.
I get what you mean, and it would be cool if uni students could get free train passes, but i dont see it coming in the near future LOOOL