Procurement cost. And to be exact - powerplant still constitutes a significant part of the price(double digits).
But when we go to operation costs(and logistics load) - powerplant becomes of huge importance - the more active ship is, the costlier it gets.
That's assuming 052D can't do the same networking(or there is no 055 in TG).
Given that 052Ds are very recent ships, and their radar/cooperative engagement/battle management system development schedule proceeded at least partially in parallel with 055 - why such an assumption?
The 052D doesn't have the next generation CEC system the 055 has. This is easy to physically check --- it takes the form of four small phase arrays arranged to face all four sides and placed high in the ship. On the 055, these are mounted on near the top of the integrated mast, sandwiched between the X-band AESA and a set of four panels best guess is a new passive radar and ESM. These CEC panels might be working at 6Ghz to 18Ghz, like Wifi 6 or 5G.
These panels are nowhere to be found on the 052D or the 054A (I presume they will be on the 054B) but they are on the Shandong, and there are similarly shaped panels on the Liaoning (retrofitted after March 2019) and the Type 075. Oddly enough, they were field tested on a 054A, namely the 515 Binzhou, which carried the panels all the way to its Gulf of Aden mission, and spottable when the ship visited Greece and Turkey.
In the USN, the CEC took the form of circular arrays, possibly choke antennas, in its first and second generation. By the third generation, it takes the form of four flat panels, namely thin phase arrays.
Given that the flat tops have the CEC, they can exchange and unify their sensor data with the 055's, which is big given the great height of these ships which can cover an expanded radar horizon, couple the fact that the flat tops also have their own AESAs, and bringing other radars for the ride.
If CEC is present on the 052D and 054A, it would have to be through conventional datalinks. There are new circular domes retrofitted on the 052D and 054A along with other ships, presumably with gyroscopically stablized phase arrays to follow satellite, high flying UAV or aircraft for digital communication, but I am not sure if it does ship to ship communication, although these domes probably can allow the flat panel or phase array to go vertical enough to stare at another ship.
Also in terms of the EW, the 052D has the current PLAN "mainstream" standard with the Type 726 set, which consists of an ESM for signal and threat analysis, an ESM for directional finding, an ECM for active jamming and a DLS for passive jamming. While on the other hand, the 055 sports a brand new EW suite.
The main AESA on the 055 looks larger than the 052D, presumably rumored to be using Gallium Nitride. The ones on the 052D are presumably Gallium Arsenide, although presumably, these can be updated in the future. Another feature is that the 055 has a four panel X-band AESA for its fire control, undoubtedly multifunctional, while the 052D still relies on old school mechanical radars for its fire control, namely Type 364, 344 and 366. Even if the 052D has three radars, the X-band AESA on the 055 can track and engage multiple targets on its own, separately from the main AESAs, while on the 052D, a mechanical radar tends to track and engage a target singularly as it is limited by its mechanical shape and movement. Six turbo-generators on the 055, presumably QD50 (might be excessive??) are powering sensors, EW and communications on the 055. The main radars on the 055 seems powerful enough, that it doesn't need the VHF radars on the 052D.