What is there to experiment on this ship though that would warrant not building more! It's just a ship that carries helicopters, is it the engines or radars or electronics of the ship? I'm pretty sure they wouldn't have built two of it simultaneously without previously testing every component of it down to the smallest screw, they wouldn't have built 2 at the same time if they weren't 100% sure that the design of the ship and every part of it was flawless, you do not produce two 35k ton warships simultaneously if you need to test something on it, especially not China.
That is why I believe the one & only possible reason as to why they aren't building more at the moment is because the drydock is currently occupied by other ships.