Why is Tom Robinson found guilty, even though the evidence clearly indicates he is innocent? To Kill A Mockingbird

In To Kill a Mockingbird, Tom Robinson is not guilty of anything. He is accused, by Bob and Mayella Ewell, of raping Mayella. But it seems abundantly clear that Mayella and Bob are lying and that Tom is completely innocent of any crime. When Atticus questions Bob Ewell on the stand, he makes it clear to note that Mayella had a wound on her right eye and had wounds all around her neck. Therefore, it would be more likely that someone with two good working hands who is also left-handed was likely to be the attacker. Bob Ewell is left-handed with two good working hands. Tom has only one good working hand, his right, and his left hand is basically useless due to an accident with a cotton gin. Given the testimony and this evidence and the fact that it was well known that Bob beat his children, including Mayella, it is fairly clear that Bob was probably Mayella's attacker and that she conspired with Bob to blame Tom for everything, knowing that a black man in 1930s Maycomb was likely to get convicted in spite of any evidence that might suggest his innocence.