Your jungler forgets smite...

His map pressure is down, objective control on your team is nonexistent and at least one champion on your team is going to be consistently down.

On the other hand the enemy team is now that much more predictable. They will invade and become easy to catch out. They will prioritize the objectives that they have the upper hand with. They will ward aggressively, neglecting their own jungle. They will feel safer and thus take riskier plays. All of these behaviors can be predicted and countered. Your jungler should prioritize wards and sweeping. They should buy . Your team should respond to pings for help and punish the enemy for invading. And your team should prioritize killing the enemy jungler, and ensuring that the scuttle crabs are under your teams control. If you lose it is not just because you jungler forgot . It's because your team failed to work together to shore up that weakness effectively.

I'm not saying that there is ever an excuse to not have smite as a jungler. What I am doing is giving an extreme example of the kind of thinking REQUIRED to reach any form of high level play. You should always look at the strengths and weaknesses of both teams. and you should play around them and play around your opponents playing around them. If you are not being proactive then you will not climb and you will hold others back from climbing.