Geometry Dash 2.2 is taking so long mainly because of platformer mode, the arrow trigger, and versus mode. Each of these upcoming features greatly changes gameplay, requiring RobTop to essentially rewrite a lot of the game. Simply put: the game was not designed to have icons changing direction or to have multiplayer, which is why core parts of the game likely have to be redesigned.

However, seeing the progress RobTop has via the official sneak peek and other leaks, it is clear that 2.2 is close to releasing.

In conclusion, 2.2 is taking so long because of features that require major game redesigns, including platformer mode, the arrow trigger, and versus mode.