They went to a lot of effort to cap point accumulation, since one of the major complaints about LK heroics was that people felt compelled to run them for the rewards long after they ceased being either fun or meaningful, and the consequent bad attitude dragged down people for whom the heroics were still appropriate.
Now, people are supposed to be free from that - hit the cap, get off the hamster wheel. Do some fishing. Archaeology maybe. Start a goblin alt.
And what do they find? Some people just can't get off the **** wheel. So when they run up against the cap, and have nothing meaningful to spend the points on anymore, they demand a point sink so that they can run a few more loops and still accumulate stuff.
That's all this is. It's not cost-effective because it's not meant to be. In fact, the prices /should/ be a big neon sign saying "Are you really sure that you should be doing this?"