Well that makes sense. A representative of an Axis power (administrator) should be able to stop someone from freely using that power. Even without using shinsu or light Urek was able to destroy said pseudo-admin with ease. Baam was only able to use shinsu due to having a tool that allowed him to...
Urek could be simply using the excuse of not being able to get out of the tower because none of the 10 Family Heads know the purpose of the Tower besides Zahard.
I’m assuming that he knows his interference would affect the story of the axis to be, so he told the FH’s he would not get involved. & even when he does get involved he plays by the tower’s rules so not to affect the story.
I like this theory better. Zahard’s arrogance shows because he always says he has the seeds of a King within him. He probably comes from a faction outside the tower with many axis candidates, but he was the most promising.