This might seem counter-intuitive, but people do Ranked PvP simply because they might lose rank. Nothing is more engaging then having something you believe you have to defend. When you make it so a person has something to defend (rank), they will try very, very hard not to lose it. For KI, this translates to increased profits, because players will hatch more, get more snacks, get more packs, create more characters.
If you aren't satisfied with the ranking system, there is a practice PvP that doesn't log stats like rank. You can play purely for fun.