I agree with ur point. ЁЯСМ
It's not only Vskp-Ltt & Samata express , all the other trains coming from Titlagarh / Vishakapatnam side takes 1:30 hrs / 2 hrs to reach Raipur junction.
But...
more... if u see trains departing from Raipur junction towards Mahasamund / Titlagarh / Vishakapatnam takes only 58 minutes to 1 hr only to reach Mahasamund station.
Three reasons which I found could be as mentioned below :
1 - Raipur junction comes in Mumbai - Howrah main line so trains coming from loop line ( Titlagarh/ Vishakapatnam side ) does not get much importance / attention as compared to trains coming from Bilaspur side.
2 - Platform availability at Raipur Railway Junction could also be a reason.
3 - Slag time due to goods trafficking can be a reason for this.