Most shots received will be from dead ahead. Any tank against modern round is likely dead from other angles as well. Makes sense to save that weight. I refuse to believe these designers could be so insanely stupid for so many generations. There must be a reason and the likely reason is this. Chinese tanks will likely only ever face some of the strongest most updated modern western tanks in a tank on tank fight. Tank on gunship, gunship wins. Tank on infantry, possible top, bottom, side, back shot so dead anyway unless the army doesnt mind 70T tanks. Facing modern western tanks, any shot to the side is also dead. Therefore why not just reinforce the most likely to be hit section while keeping weight down. Keep in mind that while the Chinese tanks have abysmal armour everywhere except the dead on front, the front armour is sloping and is angled. Take a look from top views of factory tanks before wedge bracket is installed. So in some ways they are behind a armour shape that sort of "surrounds" them, albeit nowhere as convincingly as soviet designs. Abrams and challenger has similar turret geometry. It's just that they have 10 tonnes more armour and very advanced composite armour. Abrams were still very easily killed from the back, and side, also bottom until the developed ways around IEDs. Most of these kills were friendly fire but that still shows a well made round from a NATO 120mm L44 can easily penetrate M1 side armour. I doubt PLA can't do this with 125mm, higher muzzle velocity, higher chamber pressure... even if the sabots are slightly shorter. This means that in many cases against advanced enemies, extra side armour is dead weight. Against less capable foes, it certainly pays to have good all round armour though. I feel like PLA is custom building all its forces specifically against US equipment. Drones and gunships are overall more effective than tanks and more money should be spent there.