Can we talk about feast or famine?

I am kind of frustrated and at a loss for words. You can beat someone through laning phase, sure, fine. You can beat them a few times in teamfights too, sure alright. BUT, i can not see how it should be possible to basically annihilate someone in lane throw them into like 1/8 and then suddenly they get a few kills bot and snowball into hell. Why is that a thing? Is it for more fun, interactive gameplay? The whole reason someone focuses so hard on shutting someone down is for how stupid the champion's late is, i just dont understand why its okay.