Devoe has a really high release point with his shot - up over his head. Because of this he actually has a more difficult time the closer he gets to the basket with a jump shot.
The best FT shooters have a lower release point. For example, one of the better FT shooters of his day, Jeff Hornacek had a lower release point. Westbrook also does - out in front of his body as opposed to over his head. Terrell Brandon hardly ever missed a FT - again, shot was out in front of his body and not over his head. Even a bigger guy like Joe Krabbenhoft - shot around 90% from the line last year - lower release point.
FT shooting is mental, sure, but it also has a lot to do with technique and how you shoot it.