Peace ramesha
Those who mourned had lost their loved ones they could not stop themselves. You and me are on the side of the people who mourned the loss of the great saints.
However, today to mourn once a year is like remembering a past event that was not any of our doing and that moment was but a dark time in history, but today these very people those saints are alive in heaven. Why remember their temporary condition when you can remember their permanent one?
Wasalaam Psyah, if one remembers Imam Hussains' sacrifice only "once a year" then i am not sure to what extent s/he is fulfiling obligations set upon him/her as a Muslim by the Allah Almighty and his Prophet. Unfortunately though I think large majority of us have forgotten the Ahlul Bayt and that is why we as Muslims are in a state that is quite shameful to say the least.
Allama Iqbal said:
Insaan ko bedar tou ho lenay dou
Har qaoum pukaray gi humaray hein Hussain