The alotted time for this trial is not yet complete. Satan has been loosed for a time and the testing is not yet over. Just as Judas was allowed free reign to betray Christ, so modern day Judases are given free reign to betray Christ's Mystical Body.
That's the theological answer.
The practical answer is that Mahony is a clever operator. He sails close to the wind and is nuanced and careful about his deconstruction of the faith. Take the present incident, for instance. What could he be nailed for? The article states that gays were "welcomed in LA". So? He can argue that it's the Church's job to welcome all those who feel drawn to her. Note that Communion was not given to anyone in a Rainbow Sash. Thus, he can rightly claim that he has done nothing in contravention of Cardinal Arinze's directive, if indeed it even was a directive. There were no Rainbow Sashes, no incidents, no confrontation. Just a Pentecost Mass at which there were present unidentified homosexuals. He could claim that this situation is repeated in every diocese.
That's typical of Mahony.