Of course they did it to make money. That said, I just think it's silly that people act entitled to any additional content whatsoever. When you purchased Wings of the Goddess, new endgame was never promised in that package. More importantly, when you purchased Wings of the Goddess, there was absolutely concept of content geared towards beyond level 75. Why shouldn't we have to pay for additional content to accompany the level cap?
The monthly fee pays for a lot of thinks. Development of new content is only one of many. I don't think the fees we pay each month go quite so far as adding content beyond a level cap which has existed for the past six-and-a-half years is covered.
I expect Vision of Abyssea to be worth $10. As far as I'm concerned, $10 really isn't all that much money; and I'm willing to shell out $30 for new endgame that will keep us going until level 99. If you don't think it's worth that amount of money, that's fine, don't buy it. I just think it's silly that you seem to think it should be free.