I don't think he mourns over Satan either.
The problem is about what "you ("I") don't think". God's ways are not the ways of fallen men. God is the God of compassion. God is love, not indifferent. He will understand of all, that which others cannot understand, the loss of the one/s which of themselves chose to be lost when they did not have to be.
You do not understand the character of God as it is written in scripture, in that Lucifer was once the closest created being to God that God ever made (Isaiah 14; Ezekiel 28), being personally the representative of God's character to the unfallen universe. The created son that was favoured above all.
God Himself placed Lucifer next to Him.
Eze 28:14
Thou art the anointed cherub that covereth; and
I have set thee so: thou wast upon the holy mountain of God; thou hast walked up and down in the midst of the stones of fire.
God will bring to pass His strange act:
Isa_28:21 For the LORD shall rise up as in mount Perazim, he shall be wroth as in the valley of Gibeon,
that he may do his work, his strange work; and bring to pass his act, his strange act.
Eze 28:19 All they that know thee among the people shall be astonished at thee: thou shalt be a terror, and
never shalt thou be any more.
Lucifer was the "friend" that betrayed God in the most indepth way.
Psa 41:9 Yea,
mine own familiar friend, in
whom I trusted, which did eat of my bread, hath
lifted up his heel against me.
Both Lucifer and Judas are "sons of perdition".
Lucifer will be reminded, in Rev. 20, of all the times before he chose rebellion (without a cause), and admit God is true:
Isa_45:23 I have sworn by myself, the word is gone out of my mouth in righteousness, and shall not return, That unto me
every knee shall bow, every tongue shall swear.
Rom_14:11 For it is written, As I live, saith the Lord,
every knee shall bow to me, and every tongue shall confess to God.
Php_2:10 That at the name of Jesus
every knee should bow, of things in heaven, and things in earth, and things under the earth;
Eze_18:32 For
I have no pleasure in the death of him that dieth, saith the Lord GOD: wherefore turn yourselves, and live ye.
Eze_33:11 Say unto them, As I live, saith the Lord GOD,
I have no pleasure in the death of the wicked; but that the wicked turn from his way and live: turn ye, turn ye from your evil ways; for why will ye die, O house of Israel?
Pro_24:17
Rejoice not when thine enemy falleth, and
let not thine heart be glad when he stumbleth:
Pro 24:20 For there shall be no reward to the evil man;
the candle of the wicked shall be put out.