यमला-पगला-ट्रेन का-दिवाना - कार्तिक

He is referring to the train earnings mentioned in the Bibek Debroy committee's report from last year ( Check page 32 for earnings from Raj, Shatabdi and Duronto trains).
click here
And also he is referring to profit, not revenue. DBRG Raj has more revenue than BCT Raj, but has more operating cost also, so it is running in losses. In that way, PNBE Raj is second in terms of profits.
...
more...

Kerala exp runs for a very long distance, and hence operational costs are very high, while revenue will not be as high as a Rajdhani as it is just a normal SF, so profits will also be less. Also, there will be a lot of maintenance cost also due to the requirement for 6 rakes ( + spare rake). Long distance doesn't mean more profits.
It's still an awesome train nonetheless. :)