Why didn't the Qur'an simply abolish slavery?

۞ لَّيْسَ ٱلْبِرَّ أَن تُوَلُّوا۟ وُجُوهَكُمْ قِبَلَ ٱلْمَشْرِقِ وَٱلْمَغْرِبِ وَلَـٰكِنَّ ٱلْبِرَّ مَنْ ءَامَنَ بِٱللَّهِ وَٱلْيَوْمِ ٱلْـَٔاخِرِ وَٱلْمَلَـٰٓئِكَةِ وَٱلْكِتَـٰبِ وَٱلنَّبِيِّـۧنَ وَءَاتَى ٱلْمَالَ عَلَىٰ حُبِّهِۦ ذَوِى ٱلْقُرْبَىٰ وَٱلْيَتَـٰمَىٰ وَٱلْمَسَـٰكِينَ وَٱبْنَ ٱلسَّبِيلِ وَٱلسَّآئِلِينَ وَفِى ٱلرِّقَابِ وَأَقَامَ ٱلصَّلَوٰةَ وَءَاتَى ٱلزَّكَوٰةَ وَٱلْمُوفُونَ بِعَهْدِهِمْ إِذَا عَـٰهَدُوا۟ ۖ وَٱلصَّـٰبِرِينَ فِى ٱلْبَأْسَآءِ وَٱلضَّرَّآءِ وَحِينَ ٱلْبَأْسِ ۗ أُو۟لَـٰٓئِكَ ٱلَّذِينَ صَدَقُوا۟ ۖ وَأُو۟لَـٰٓئِكَ هُمُ ٱلْمُتَّقُونَ

It is not righteousness that ye turn your faces to the East and the West; but righteous is he who believeth in Allah and the Last Day and the angels and the Scripture and the prophets; and giveth wealth, for love of Him, to kinsfolk and to orphans and the needy and the wayfarer and to those who ask, and to set slaves free; and observeth proper worship and payeth the poor-due. And those who keep their treaty when they make one, and the patient in tribulation and adversity and time of stress. Such are they who are sincere. Such are the Allah-fearing.

وَمَا كَانَ لِمُؤْمِنٍ أَن يَقْتُلَ مُؤْمِنًا إِلَّا خَطَـًٔا ۚ وَمَن قَتَلَ مُؤْمِنًا خَطَـًٔا فَتَحْرِيرُ رَقَبَةٍ مُّؤْمِنَةٍ وَدِيَةٌ مُّسَلَّمَةٌ إِلَىٰٓ أَهْلِهِۦٓ إِلَّآ أَن يَصَّدَّقُوا۟ ۚ فَإِن كَانَ مِن قَوْمٍ عَدُوٍّ لَّكُمْ وَهُوَ مُؤْمِنٌ فَتَحْرِيرُ رَقَبَةٍ مُّؤْمِنَةٍ ۖ وَإِن كَانَ مِن قَوْمٍۭ بَيْنَكُمْ وَبَيْنَهُم مِّيثَـٰقٌ فَدِيَةٌ مُّسَلَّمَةٌ إِلَىٰٓ أَهْلِهِۦ وَتَحْرِيرُ رَقَبَةٍ مُّؤْمِنَةٍ ۖ فَمَن لَّمْ يَجِدْ فَصِيَامُ شَهْرَيْنِ مُتَتَابِعَيْنِ تَوْبَةً مِّنَ ٱللَّهِ ۗ وَكَانَ ٱللَّهُ عَلِيمًا حَكِيمًا

It is not for a believer to kill a believer unless (it be) by mistake. He who hath killed a believer by mistake must set free a believing slave, and pay the blood-money to the family of the slain, unless they remit it as a charity. If he (the victim) be of a people hostile unto you, and he is a believer, then (the penance is) to set free a believing slave. And if he cometh of a folk between whom and you there is a covenant, then the blood-money must be paid unto his folk and (also) a believing slave must be set free. And whoso hath not the wherewithal must fast two consecutive months. A penance from Allah. Allah is Knower, Wise.

وَلْيَسْتَعْفِفِ ٱلَّذِينَ لَا يَجِدُونَ نِكَاحًا حَتَّىٰ يُغْنِيَهُمُ ٱللَّهُ مِن فَضْلِهِۦ ۗ وَٱلَّذِينَ يَبْتَغُونَ ٱلْكِتَـٰبَ مِمَّا مَلَكَتْ أَيْمَـٰنُكُمْ فَكَاتِبُوهُمْ إِنْ عَلِمْتُمْ فِيهِمْ خَيْرًا ۖ وَءَاتُوهُم مِّن مَّالِ ٱللَّهِ ٱلَّذِىٓ ءَاتَىٰكُمْ ۚ وَلَا تُكْرِهُوا۟ فَتَيَـٰتِكُمْ عَلَى ٱلْبِغَآءِ إِنْ أَرَدْنَ تَحَصُّنًا لِّتَبْتَغُوا۟ عَرَضَ ٱلْحَيَوٰةِ ٱلدُّنْيَا ۚ وَمَن يُكْرِههُّنَّ فَإِنَّ ٱللَّهَ مِنۢ بَعْدِ إِكْرَٰهِهِنَّ غَفُورٌ رَّحِيمٌ

And let those who cannot find a match keep chaste till Allah give them independence by His grace. And such of your slaves as seek a writing (of emancipation), write it for them if ye are aware of aught of good in them, and bestow upon them of the wealth of Allah which He hath bestowed upon you. Force not your slave-girls to whoredom that ye may seek enjoyment of the life of the world, if they would preserve their chastity. And if one force them, then (unto them), after their compulsion, lo! Allah will be Forgiving, Merciful.

فَإِذَا لَقِيتُمُ ٱلَّذِينَ كَفَرُوا۟ فَضَرْبَ ٱلرِّقَابِ حَتَّىٰٓ إِذَآ أَثْخَنتُمُوهُمْ فَشُدُّوا۟ ٱلْوَثَاقَ فَإِمَّا مَنًّۢا بَعْدُ وَإِمَّا فِدَآءً حَتَّىٰ تَضَعَ ٱلْحَرْبُ أَوْزَارَهَا ۚ ذَٰلِكَ وَلَوْ يَشَآءُ ٱللَّهُ لَٱنتَصَرَ مِنْهُمْ وَلَـٰكِن لِّيَبْلُوَا۟ بَعْضَكُم بِبَعْضٍ ۗ وَٱلَّذِينَ قُتِلُوا۟ فِى سَبِيلِ ٱللَّهِ فَلَن يُضِلَّ أَعْمَـٰلَهُمْ

Now when ye meet in battle those who disbelieve, then it is smiting of the necks until, when ye have routed them, then making fast of bonds; and afterward either grace or ransom till the war lay down its burdens. That (is the ordinance). And if Allah willed He could have punished them (without you) but (thus it is ordained) that He may try some of you by means of others. And those who are slain in the way of Allah, He rendereth not their actions vain.

وَٱلَّذِينَ يُظَـٰهِرُونَ مِن نِّسَآئِهِمْ ثُمَّ يَعُودُونَ لِمَا قَالُوا۟ فَتَحْرِيرُ رَقَبَةٍ مِّن قَبْلِ أَن يَتَمَآسَّا ۚ ذَٰلِكُمْ تُوعَظُونَ بِهِۦ ۚ وَٱللَّهُ بِمَا تَعْمَلُونَ خَبِيرٌ

Those who put away their wives (by saying they are as their mothers) and afterward would go back on that which they have said, (the penalty) in that case (is) the freeing of a slave before they touch one another. Unto this ye are exhorted; and Allah is Informed of what ye do.

فَكُّ رَقَبَةٍ

(It is) to free a slave,