I don't know for sure. Maybe long distance trains are getting wap4/5/7 and wdp4, or maybe due to other reasons. But, on many occasions I have seen 11009/12123/11007 getting hauled by Wap4 & Wap7 and WDP4D too.
Priority of long distance trains maybe another reason too.
From...
more... 22/06/22, 12123/12124 are getting LHB coaches replacing old ICF coaches, we can expect regular deployment of WAP 4/5/7 or WDP4D.