Because the previous day's 12238 ki rake is used for next day's departure of 12237 from Varanasi post PM. Since 12238 would have been delayed 18+ ghante, it would have reached Varanasi on the morning of 12237's departure. The additional delay is just to accommodate for PM for the train.

Pata nahi kyun yeh train abhi tak LHB mein nahi badli gayi hai,

1. Don't take this train if you're with older folks 2. This train is usually on time, thanks to its VIP status 3. Avoid the side berths in 2nd AC unless you really want 'em 4. Toilets are a mess, avoid if possible 5. Bring headphones unless you dig train noises, this one's pretty loud and clear

Mere safar ke baad mere is train ke liye tips
1. Iss train se bhaago agar senior citizens ke saath travel kar rahe ho
2. Train har din almost time pe chalti hai kyunki isko route mein excellent priority milti hai
3. 2nd AC mein safar karte waqt side lower ya upper se bacho, until aapko khaas jarurat ho (ticket book karte waqt preference dena)
4. Bathrooms sirf showpiece ke liye hain, har bathroom choke ho jata hai aur paani 2nd AC aur 1st AC mein bahar aata hai, 3rd AC mein toh bhool hi jao sleeper ke baare mein
5. Earphones lekar aana, agar ICF coaches ki awaaz sun'na pasand nahi hai toh kyunki insulation bekar hai aur awaaz kaafi andar aati hai, coach ke beech mein na ho toh chordo