My understanding is the fallen angels never beheld the Beatific Vision. At their creation they chose to defy God and, being 100% spiritual beings, were fully aware of all the consequences of that decision and chose that way nonetheless. This caused their entire being to be entirely corrupt and evil, with no chance of change.
The reason we humans are capable of sinning and repenting is because we have both spiritual and physical natures. Our physical nature can blind us to what we really want (like when a Christian sins and regrets it), if we then go on to repent we can atone for that past sin through Christ’s propitiatory sacrifice.
Unlike us, there is no salvation for fallen spiritual beings - they weren’t temporarily blinding like a human can be by lust, but rather made their decision with full disclosure, so to speak.
Satan continues to defy and fight God out of pride. That is what led to his fall, he was too proud to humble himself before God, so he took on an evil spiritual nature and was cast from Heaven by the angels loyal to God. From what I’ve heard supposedly before the fall Lucifer was the greatest of the angels, but instead of serving God - which would have made him truly great - he got full of himself and opposed God.
Something that is at least somewhat relevant to this conversation: the difference between Satan and Lucifer…I had always though Satan was just Lucifer after the fall, but I’ve heard from at least one exorcist that they are two different beings (Fr. Malachi Martin describes Satan as the liar with the twisted tongue and Lucifer as the attacker, or something along those lines). Thoughts or information?