There are many things to be said as to why the Night of Qadr has been named as such:
1- The Night of Qadr has been given this name because the destiny and all the things that will happen for a human being during that coming year are decided during that night. Confirmation of this meaning can be found in the 3rd and 4th verses of Surah Dukhān which state: “Indeed We sent it down on a blessed night, and indeed We have been warning [mankind]. Every definitive matter is resolved in it”
This verse is in line with various traditions which state that the destiny of the people is decided on that night. Whatever is going to come in the form of sustenance, one’s lifespan, and other such matters are set on that night. At the same time, this concept has no contradiction with the free will and decision making of the people. This is because the destiny of people is set according to their worthiness and capabilities; their faith, piety, purity in intention, and actions are all part of the equation. Each person is destined for what he or she is worthy of based upon their actions, faith, and other such components. So the people strive with their own efforts and this allows them to be given a certain type of destiny and future, whether that is good or bad. It is due to this reason that such a concept has no contradiction with that of freewill.
2- Some people have said that the Night of Qadr has been named as such because it is a worthy and magnificent night. The 74th verse of Surah Ḥajj mentions the following: “They do not regard Allah with the regard due to Him.”
3- It is sometimes said that the naming is due to the power and station of the Quran which was revealed to the Prophet (ṣ) through the medium of Angels.
4- Or that it is a night wherein the Quran was decreed to be revealed.
5- Or that the one who brings alive this specific night becomes the master of destiny, rank, and station.
6- Or that on that night the angels are revealed to such a large degree that the earth because filled with them (the earth becomes tight with them in a sense). This is because the word ‘Taqdīr’ also has the meaning of becoming tightened, just as it can be seen in the following verse: “…and let he whose provision has been tightened spend out of what Allah has given him…”
While the first
understanding is the strongest one, it is possible to also collect all of these
various interpretations and combine them into a unified whole.
 Surah Dukhān, verse 3 and 4: «إِنّا أَنْزَلْناهُ فی لَیْلَة مُبارَکَة إِنّا کُنّا مُنْذِرینَ * فیها یُفْرَقُ کُلُّ أَمْر حَکیم»
 «ما قَدَرُوا اللّه حَقَّ قَدْرِهِ»
 Surah Ṭalāq, verse 7: «وَ مَنْ قُدِرَ عَلَیْهِ رِزْقُه»
 Taken from the text: Tafsīr Nemūneh, Ayatullah Makārim Shīrāzī, Dār al-Kutub al-Islāmīyah, 36th Edition, vol. 27, p. 210.