Noob Questions: What Determines A Champion's Lane?

Everyone always says that a champion goes top, mid, jungle, etc. But i'm unclear on what determines which lane or role a champ fills. I know the roles and who fills them (Tanky DPS top, Bursty AP Caster mid, fast sustained DPS in Jungle, ADC and Support bot) but i feel like it's important to know why the roles are what they are so you can understand when that isn't the case or read the meta. All i know is that supports go bot to support kills for an ADC and junglers are what they are to farm efficiently. Thanks in advance.
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