If we compare WAP5 with WAP7 then cost is one major factor, WAP5 production cost is much more compare to WAP7.
Basically CLW manufactures WAP5 for MU'ed purpose for future planning but still it is on paper, Another issue with WAP5 is Wheel slip for gradient.
Whatever it is, but all 3 phase loco are easy for driving( No tap Changer) & regenerative braking system.