First of all, unlimited power is held by God. The existence of any and every other thing was and is by Him, yet He doesn't practice an autocratic kind of leadership, and even if He chooses to do, no one has the right to question Him. He gives everyone the opportunity to make choice.
What is choice? It's an option, an opportunity to select from a variety.
Now, one unique thing God gave man is free will. The right to make our own choices, and whatever we decide to choose, He doesn't force us to do otherwise. He only cautions, corrects and commands but never does He confront, counter or control us against our will.
Wouldn't it then be unfair that He gave us free will, or free choice, but with no choices? He commanded them (Adam and Eve) "not to", but their free choice would be pointless if His voice was the only voice they ever heard.
So, Satan went to voice his own suggestion and he was allowed, that they might have choices. Take note, he was only allowed to voice and not to force them. It was left for them to accept his suggestion or hold on to God's instructions. They eventually chose Satan's over God's, and how was that supposed to be God's fault? Not that He hid the implication of disobeying Him from them.
Who knows, could it be that free will was given in heaven, which was why Lucifer (Satan) even conceived the imagination to overthrow God in the first place? Else, why would anyone in heaven ever think about overthrowing God? Not just him who thought about that but him and his crew. That means he (Lucifer) actually talked to them (fallen angels) about it and they joined forces with him to carry out the mission. Though God can't in any way be overthrown, but in order words, a coup was actually planned in heaven. This is serious! I could imagine Him looking at them planning it. Time doesn't exist in heaven, but I think he (Lucifer) mapped out a lot of strategies as to how to go about it, maybe placing his followers at various strategic corners of heaven. And maybe as they were about to strike, God then took action. He would have stopped the plan at the initial, but it could be that He wanted to see if they would have a change of mind.
They became fallen angels, just like man fell from glory in the garden.
Like I mentioned earlier, God has every right to make decisions and force everyone to obey them, and no one would dare question Him. However, He chooses to let us be, to let us have the freedom to do whatever we want. That doesn't make Him weak, or stupid, or in any way insensitive to the happenings in the world. He is just! And you know what justice means, in one aspect? The state of being fair!
He is fair, yet firm. He is just, yet steadfast.