Why would PLAN want more 054AG when 054B is already in production? What is the logic?
Several reasons that I came across:
#1 - Due to the present geopolitical development and the heightening risks of war in the WestPac, the PLAN very much needs the required quantity to hold the front for the time being - The sooner, the better. In this context, the 054A/AGs are cheaper and easier to build quickly in larger quantities than the newer 054Bs.
#2 - Significant portions of warfighting in a WestPac war for the foreseeable future are expected to be done within and around the 1IC, of which the 054A/AGs are certainly more suited to operate in.
#3 - The 054B, while retaining (much of) the mature weapon systems from the 054A, is still quite new when it comes to the radars, sensors and the propulsion systems onboard. Some amount of time will be needed to configure, calibrate and rectify any faults that may come with the newer and unproven systems onboard the present 054B twins before the PLAN is satisfied with the 054B for said class to enter mass production.
#4 - With nearly two decades worth of experience in building 054A/AGs, it would be easier for Hudong-Zhonghua and Huangpu-Wenchong to keep building the 054A/AGs while waiting for the processes in #2 to be completed. In the meantime, those two shipyards can also begin the gradual, full transition of their shipbuilding workforces from 054A/AG-construction to 054B-construction.
#5 - More 054A/AGs meant that more PLAN cadets can be trained and brought up to speed onboard the 054A/AGs before being assigned to the newer 054Bs in the coming years once the two shipyards started churning them out.
However, it should be noted that this is not to say that only 2x 054Bs will be built for the first batch, let alone the notion whereby only 2x 054Bs will ever be built.