Angels are a different species from us with different natures.
As far as I understand it like they are Binary. Originally made Mono-polar to work and live in God’s presence. Then before God revealed Himself there was a violent rebellion all the way up to rank of Cherubim down consisting of a third of the Angels.
Next one needs to consider it is believed that they are born with intrinsic knowledge knowing all that they need for their function, and that you had a rebellion by individuals who had intrinsic knowledge of God’s plans.
Add to that Christ mentioned that to “Blaspheme the Holy Spirit” (which is often believed to mean that attributing those who saw Christ then attributed his power to be from Satan thus insulting God, his Son, and the Holy Spirit at once) is an unforgivable sin. This sets a legal precedent that God will not forgive certain acts. Meaning irrevocable banishment from Heaven. Also mentioned by Christ as eternal punishments and in Revelations that the Lamb (Christ) will remove from the those condemned to hell from book of life.
Next we add knowledge and accountability. We are born ignorant and God remains fairly mysterious to us Angels knew everything about God and were created in Heaven. If you research the various ranks you would see that by the Rank of Cherubim it would be like a several members of the Presidents Cabinet rebelling against a President. So full knowledge, violent rebellion, multiple attempts to disrupt God’s plans, attempted corruption of Christ, and according to Christ he is a murderer and a liar so quite possibly counts of Heavenly Homicide.
So while they were once mono-poles made to work in the light and power of God they are now cast out of Heaven into Hell (which God created for them as a detention area) becoming binary beings. However their stint in Hell is only temporary. They are basically prisoners banished from heaven awaiting trial (The Final Judgement) They are allowed to roam the yard (Earth) but if they fight a guard (Angels loyal to God) they lose and are tossed back into Hell. People have free will and need to ask a guard for assistance and ask for others protection as well.
Also forgiveness comes on the merits of Christ, his life and Crucifixion. Considering he is the King of Angels and that they rebelled against Christ and not wanting to serve God it poses a problem for forgiveness. The theologian Origin believed angels were in flux others since then have stated it is fixed.
Peace