Sforno on Leviticus 21:6/ספורנו על ויקרא כ״א:ו׳

1ולא יחללו שם אלוקיהם, even though all of the aforementioned were expressions of grief over the loss of relatives, the priest is not permitted to disregard the dignity which his status as priest imposes upon him. Even though the priests, no doubt, mean to honour G’d in what they are doing, when they disregard the restrictions their status imposes upon them, they indirectly desecrate the name of the Lord.