An answer may be found in the fact that Paul had fear. Fear of who could listen him and react accordingly. They were powerful spiritual beings, since in any moment they could even rape the Christian women.
1 Corinthians 11:10 :
10 It is for this reason that a woman ought to have authority over her own head, because of the angels.
So Paul was moved to silence. If the demons could know from him the fact that they had killed just the Son of God, then they would have repented before the end, so God couldn't destroy them completely for their sins. They would be left in their place, still in possession of the world. God wanted that they remained in the obscurity about the fate of the Son of God. They would have realized only that Paul was preaching a “crucified Christ”, but without knowing basically where and when this Christ was crucified.
The silence of Paul was a military silence. Part of the his war against the “archons of this age”.
Now, since Paul himself says that the his war was “not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places” (Eph 6:12) - a passage that succeed fully to sound pauline despite of being written by a false Paul - the silence of Paul couldn't be caused by earthly rulers, just as the veil was required by him for the women not against the lust of men, but “of angels”.