WWE advertised plenty of people for the Royal Rumble match. They didn’t deliver on all of them.
WWE advertised Heavy Machinery, Buddy Murphy, Rusev and Bobby Lashley for the match. Kane also made it pretty clear that he would be in the match as well. He didn’t show up either.
It’s unclear why WWE switched so many people around. They ended up having 30 men for the Royal Rumble match anyway, but they had to rearrange some things first.
Perhaps we’ll eventually find out some grand reasoning why those men were left out of the Royal Rumble match. Until then we can just continue to wonder “What if.”