That's not a particularly great example. Unity launched at 3x the price and was (rightfully) curbstomped everywhere for its bugs and glitches at release. VC has also reached a discounted price of $5 during sales, while Unity has gone to a low of $30. Despite this large difference in price, VC sold only a little more than double what Unity did. Point being Unity actually grossed more money, despite the fact that every outlet on the planet was declaring the game a complete mess. There's also all of the Uplay sales that are unaccounted for (No clue if that is a sizable number or not)
Like - I would love for every single DQ game to show up on Steam; I'm just pointing out that you're falling into the common mistake of presuming that these things will turn a huge profit and Square Enix is just too stupid to realize it. We can't pretend to understand how much money it costs to port a Dragon Quest game to PC. We also can't pretend to know just how well it would sell, especially when Final Fantasy - a much more popular series in the west, did not put up particularly mind blowing numbers. Only FF7 sold extremely well, and that's because it's FF7.
Hopefully the game being made in Unreal Engine 4 will increase the chances they give it a shot on PC.
(Edit - found this random snippet of trivia by happenstance:
https://twitter.com/steam_spy/status/610089846166654976 that means 33% of the sales for VC were when the game was at $5. I'm sure it was still quite profitable all things considered, but these jRPGs aren't sales titans on steam)