The parsing of the question raises the issue of middle knowledge. Also at stake is the matter of the origin of evil; the SEP also includes an extensive, relevant article on evil in general. Carl Jung's Answer to Job is another hauntingly insightful source of reflection on this topic.
Now, offhand, the ChristianitySE might be a "better fit" for the question; BiblicalHermeneuticsSE is another option. The Catholic Church has a rich dialectical tradition, however, and I would suspect that you'd have a higher chance of receiving an informed Catholic response on the former SE rather than the latter (scriptural hermeneutics are more a preoccupation of Evangelical and Reformed Christians, I think; hence answers on that SE would tend to be shallower than you're looking for).
But at any rate, I went through a long Catholic phase (my personal faith story is sort of like the reverse of Father Elijah's from Michael O'Brien's Children of the Last Days books), so I will offer my sustained answer on the basis of my familiarity with Catholic demonology/hamartiology.
The question of why Satan fell is unsettled, in this context. The gist of the problem is:
And in the first place what was the nature of the sin of the rebel angels? In any case this was a point presenting considerable difficulty, especially for theologians, who had formed a high estimate of the powers and possibilities of angelic knowledge, a subject which had a peculiar attraction for many of the great masters of scholastic speculation. For if sin be, as it surely is, the height of folly, the choice of darkness for light, of evil for good, it would seem that it can only be accounted for by some ignorance, or inadvertence, or weakness, or the influence of some overmastering passion. But most of these explanations seem to be precluded by the powers and perfections of the angelic nature. The weakness of the flesh, which accounts for such a mass of human wickedness, was altogether absent from the angels. There could be no place for carnal sin without the corpus delicti. And even some sins that are purely spiritual or intellectual seem to present an almost insuperable difficulty in the case of the angels.
How could Satan, if he was the highest and hence wisest of the angels, possibly have been foolish enough to think that he could usurp God? Even equality with God should have seemed impossible, in his eyes; much less, then, superiority over the divine nature.
One could take this for a demonstration of the absurdity of the doctrine of Satan, then. Or one could invoke other passages from the Catholic textual tradition to look for a deviant solution to the problem.
For one, then, the Catholic Bible says that God did not create death, and that death entered the world through the envy of the Devil, and that death does these kinds of things modulo a covenant that it makes with the wicked. Also, Jesus Christ mysteriously asserted that blasphemy against the Holy Spirit is the "eternal sin," so arguably, that must've been the sin that Satan committed par excellence. Moreover, the Catechism of the Catholic Church says that the Spirit's lowkey self-presentation is an example of divine humility. Putting all these strands together, I think we can form the following narrative picture:
God is not the only uncreated being. God is the uncreated Creator/Creatrix, but there is also an uncreated Destroyer, Apollyon, Death with a capital "D." Though not as powerful as God, Apollyon is mythopoeically cognate with beings like Apophis and the Typhon from other demonologies. As far as Christianity goes, it is Death ("and" Hell) that is cast into the Lake of Fire after Satan is (so says the Revelation timeline), and Paul says that death is the last enemy to be vanquished. The Catholic Bible's footnotes indicate that it is Apollyon who binds Satan during the Millennium.
So God cannot prevent all evil by merely wishing so: Apollyon is at least powerful enough to impend darkness upon the creation by its own nature. Satan wants to prove himself to God, prove himself faithful, by fighting evil. Satan knows that God is humble, and that humility is relevant to fighting evil. Satan's original mistake is thinking that he can be more humble than God, then. Satan was one of the seven angels "who stand before the Lord," who are of "the sevenfold Spirit of God," i.e. whereas any human can be indwelt by the Spirit, it is the seven highest angels who alone, of all the angels, were granted to be indwelt. So Satan thought to use the power of the Holy Spirit, to fight evil in God's place, and in this, Satan blasphemed the Spirit (rather like Peter disrespected Christ by complaining about the plan of the Crucifixion, prompting Christ to rebuke Peter under the moniker of Satan).
In turn, Satan lost his indwelling by the Spirit and turned to Apollyon, making a covenant with Death, by which Death's power broke through the barrier around the creation, and so "entered the world." Again, God cannot simply wish away the Destroyer's power, but must undertake a genuinely costly plan of redemption and salvation for the creation's sake, as such.
And because Apollyon is sufficiently independent on God's wishes, perhaps God could not have ever been guaranteed to create only beings who did not fall as Satan did. Perhaps in every set of beings God might have created, there would have been one who originally fell, setting in motion the terrible chain of events just storyboarded above. Or perhaps out of love, God is willing to create every possible living being at some time or other, regardless of what those beings will do.