Some emulator development will improve performance and compatibility for all games, while some fixes more accurately emulate specific attributes of the original hardware that individual games used in a particular way.
The GameCube/Wii emulator Dolphin, which has been in open source development since 2008 (and around since 2003) only recently reached the milestone of being able to boot every single GameCube game.
Understanding the ins and outs of a piece of hardware as complex as the Wii U is a process that can take years.
