Kurt Angle’s spot in the Royal Rumble match was originally booked for Zack Ryder, according to Dave Meltzer on Wrestling Observer Radio.
The decision was made to put Kurt Angle in the match just the day before the Royal Rumble and rather than come up with something specific for him, they just inserted him into the same spot and role that was originally meant for Zack Ryder.
WWE figured that Angle would obviously get a bigger reaction than Ryder, so they put him in the spot instead.
Angle entered at #4 and lasted only 3:15. He was eliminated second (by Nakamura), after Jeff Jarrett. So the reason that WWE basically put him in a “nothing” role in the match was because the spot was supposed to be Zack Ryder’s.