Because knowledge isn't causation. If he caused thier rebellion then it would be pre programmed but that's not in scripture.
Knowledge prior to existence is causative. I.e., if God, before He creates anything, knows exactly what everyone will do, it's either because He is causing it, or he's tapping into another source that's causing it.
Think of it this way. We are causative agents. I can decide to go get a bowl of ice cream right now, walk to the freezer and dip the ice cream into a bowl. However, if God knew before I was born that I would at this particular time go and get a bowl of ice cream, it isn't because he read my thoughts or knew my general appreciation for ice cream, because those things wouldn't exist yet, UNLESS someone else besides me formed me with those particular tendencies such that on this particular day at this particular time I would have a hankering for ice cream (which I'm starting to feel, as I type). Thus, the knowledge, before I exist, of me wanting a bowl of ice cream right now would have to be causative to be true knowledge. After I exist, God can "search my thoughts" and determine before I get the bowl of ice cream that I'm about to go get it, but that's likely not a very long-term prediction, unless I have a habit of getting ice cream at this time every day.
Angels are causative agents, as is Satan. God can read their minds, no doubt, and determine what they are thinking before they act on those thoughts, but if He knew before He created them how they were all going to act, it would have to be causative, or getting the knowledge from another causative source.
If God had to get His knowledge from another causative source to know what would happen after creation, that would suggest God is NOT the most knowledgeable entity in the universe.
I like to describe these two ideas of God's foreknowledge as "Calvinism" and "Arminianism".
"Calvinism" believes God is the causative force for everything.
"Arminianism" believes there's another causative force, and God just looks at the future through a crystal ball of some sort. Now, an honest Arminian would say that God can change the future, in which case he becomes a Calvinist, because then His knowledge of the future has to depend on His causative power, rather than on some other entity's causative power.
One can easily see the conundrum here--that Arminianism devolves into Calvinism, and that Calvinism has God as the author of sin. But both assume that the future is fixed, and they are trying to understand how it works, inscribing to God attributes He doesn't deserve.