Thank you for your question. In the same way that we mourn departed loved ones out of the love and mercy for them that exists in our hearts, even if they may have been martyred, so too the lovers of Ahl al-Bayt (as) mourn the terrible tragedy that befell them (as).
That certainly does not take away from their reward, rather through God’s Mercy, their tribulation and the softness of our hearts towards them, and the mourning that is a natural consequence, has been validated and made into a worship by God. Crying for the tragedy of Imam Husayn (as) is praiseworthy and has been associated with great rewards in our scriptural literature. It is from here that the tradition of mourning finds its roots.
May you always be successful