I don't understand how updates effect champs so much.

It's been a while since I joined lol and I don't get how slight changes can effect so much. If a game changes an item or champs damage or scaling by 1-5/1-5% how does it effect so much of the game?

The only item I think I would see a difference now would be I think BotRK and it's scaling (I heard they would change it to 8 to 4%). I don't understand why a change in damage for a skill by 10 damage hurts players.