Three reasons and one solution.
1- Because there is nothing in the western world that hasn’t been gutted of all it’s meaning, and it’s transcendent value where defiling it means anything anymore. Except The Quran.
The last symbol of holiness and sacredness. Their blasphemous souls can’t bear this.
2- Because they have been filled with ignorance and hatred towards Muslims by the media, the internet, the xenophobes, the warmongers and the racists. At some point acting on their hatred becomes inevitable.
3- Because they are trying to find a fight, a cause to live for. And they chose to have their fight be dragging everyone to meaninglessness and depravity.
As a Muslim what should you do about it?
Spread the word of Allah everywhere. Never stop.
Use their hatred as fuel to spread the truth, remember that prophet Mohamed went through harder times than this. And now you have more than 2 billion brothers and sisters all over the world.
Sunlight is the best disinfectant, and the light of Allah’s word is the best way to dispel their darkness.