In the Garden of Eden, since God already knew about the fall of Adam and Eve, why couldn't he simply remove the tree from the garden?

That's a good question. To answer your question in short, God does not want to force out love from us. He wants to leave the choice to us to love him or not. Imagine God removed every source of test/temptation from our lives. Our phones would go away, people whom we love more than God would go away, internet may go away and a lot more. But God doesn't do that, instead He is looking for people who'll follow him and love him, even when there are other things. You are rejecting the option to disobey to choose to obey. And that's the same thing that happens in garden. The temptation that the devil brought, was also an opportunity to reject the words of Satan and obey God - it was a test of man's love for God. And yes, God did know that man would fail - yet he still kept the tree, to leave the choice to man and test his love. Do read the article below by got questions.