The BSB-HWH and BSB-GHY lines will share the route upto PNBE.
It maybe a practical and cost saving aspect.
The questionable aspect is routing it then via GAYA-DHN-ASN route.
The proposed route is a mess!
However...
more... even if you take the existing alignments into consideration , the PNBE-HWH via GAYA-DHN is longer than the shortest PNBE-JAJ-ASN-HWH route by 20 kilometres only. The real bottleneck is the reversal needed at GAYA, otherwise I would be pretty confident that in spite of being 20 kilometres longer the GAYA-DHN route would be the faster route...