Re: Why?
It is supposed to be a month of sadness and mourning because the Shias believe that Hz. Hussain and Hassan 
were martyred on this day so to remember them, the Shias mourn the entire month…
So in order to not trample on their sentiments, most Sunnis refrain from wishing each other a happy new year…
That however does not stop the Shias from insulting and ridiculing the beloved personalities of the Sunnis, so now most Sunnis openly wish each other a happy new year and a blessed Muharram…
Happy new year and a blessed Muharram brother…