That's because the emphasis of that parade was advanced and new.
MLRS will do a lot of the grunt work in a war, but they are not sexy or exciting like new MBTs, fighter jets, AShBMs, cruise missiles or drones etc.
Not advanced and new? Are china´s MRLS rusty? some say (no ideia at that) that they have the most powerful MRLS systems in the world. And what do understand by "sexy or exciting" ? is a criteria for inclusion in a parade?