Being living in Tamil Nadu from past 2 yrs,
I can explain why SR is ahead of WR,CR
here the overnight trains to Chennai is allocated to each major cities,most of them having 5-6 3rd ac coaches and 1-2 2nd ac coaches
And these trains run packed throughout the year, they may not show heavy waiting list,but lot of people travel in AC classes....
more...
Apart from all this SR have rajdhani, durunto, shatabdi,DD, garib rath,super AC, AC exp
Mostly the share of trains are not divided among other divisions