Mainly because today the blue rank 6 delicacy and maintenance gifts are priced around 1-3k credits on GTN, while rank 5 gifts on the fleet NPC vendors are still 5k for a blue and 10k for purples.

Recently players were selling in bulk thousands of rank 6 blues for 800 cr/pc and purples for 3k a piece.

Ofc delicacies are loved mostly by Tanno Vik, and maintenance by droids, which means the best/cheapest in training companions to the max is now trooper. It also means something is not right in those NPC prices.

I often train ship droids first and many of them to 50 with maintenance gifts, while any other regular companions are not even close to 50 due overall very high cost. I can't afford 4 mil to train a typical companion, if I have 25 characters and 8-9 companions each. Not possible to train them all, would cost me a bilion credits lol. So any decrease in prices at NPC vendors would be highly appreciated .