OK. See I am not sure about this. Still I think this is a probable reason. When I purchase tickets from PRS Counters if the booking location and journey commencing station is in the Same state For eg I have booked ticket from Sealdah PRS for travelling from Howrah to Patna. Then GST Break up is mentioned as SGST (State) 2.50% and CGST (Centre Govt) 2.50% but if the booking location is not in the same state as journey commencing station the GST break up is like IGST 5%.. So For BPT booking location first journey commencing station and the break journey commencing station may be all in different state the GST Calculations will be complicated so I guess they decided to stop it.