Ziggs' bombs will often miss even if they're on point
This is one of those things that only exists to create frustration for players. Once Ziggs' bomb starts to bounce, it's a matter of luck whether or not it hits its target. Even if it is 100% accurate, it can bounce "over" the target even though it hardly bounces at all, and should still hit the target around the waist. There is nothing more sad than watching your well-aimed bomb go right through the target.
Imagine if other skillshots followed this logic. Ahri's orb, Ezreal's mystic shot, Thresh's hook, Jayce's shock blast....these would all miss because they were apparently "too high" above the ground.