The point buy is per the PHB. It's one of the many ways of allocating your attributes (along with 3d6, 4d6 - drop lowest and the "standard set").
You should be able to get to a 17 by allocating points to 15 and then getting a +2 racial bonus (if it applies). Since no implemented race has +2 to INT, the best you can do is a 16.
However, 16 and 17 are both +3, so that shouldn't make any difference.
If you're a min/maxer, it does severely limit the "viable" race/profession combinations. Like, a Tiefling Ranger might be fun, but at best you're going to have a 15 DEX, so +2. Which is not ideal for your primary stat.
(Larian, if you read this, please implement Dispater or Glasya so we have a +1 DEX option for Tiefling!)
From a simplicity to implement and a "fairness" perspective (for multiplayer) I can see why they went with point buy. However, for single players games, there's no reason not to let somebody click "roll again" 400 times if that's what they really want to do.
