You see, I do not necessarily see it that way....but also because the amphibious assault mission via LCAC is probably not one which is as important to PLAN as it may seem, compared to the need of other ship types and aircraft.
Those Type 071s were designed to carry four LCACs. From the get go.
They now have four such vessels and only two LCAC active and another two fitting out.
Clearly, the PLAN is intending on the LCAC mission. They thought it out and built excellent vessels (at great cost) which feature that capability. So, it is clearly important to them.
Perhaps the two new ones fitting out represent an update/upgrade and if they work out, we will see more built.
Compared to other vessels (like the Type 056), LCACs are builds that can occur at several places and could be built up rapidly if the PLAN had a design they were prepared to do so with. I mean look at how quickly they are building larger, more complex, Type 056s...or for that matter, how quickly they built up the Type 22 catamaran missile FACs.
We shall see what these next two LCACs do and perhaps get a hint from that