Are there any good reasons for not using it themselves other than maybe the hard kill system isn't working as well as they would like it to?Side protection in modern day is only concerning the threat from an ATGM, any modern APFSDS will just pierce through any modern tank's side armor no matter how good your ERA or how thick it is. There's already decade old solution for this, which is the hardkill active protection system. Kinda weird that noone is suggesting this earlier, especially since PLA already has this kind of system, yet for some reason is unwilling to use it, merely for foreign export instead.
I think most threats to ZTZ-99's would be airborne munitions where the laser countermeasure would be able to engage.