Because of everything that could be broken, one that effects income is the most game changing currently. As the game decreased its overall time by 1/3rd on average since season 7. Gold income esp at early levels importance when up by 33%. So no missing that cs is 33% worse for you and your team. Add enough of those up you end up with a loss.
Ezreal negates this negitve effect and actually generates even more gold threw use of Kle than most champions with the same keystone. When mid game hits hes late game build.... only we don't have a late game anymore.... Which means you and your team at that point don't really have time to catch back up in gold, and couldnt unless ez hits full build provided they played bad enough to not win it early with such a lead. They will litterly have to throw the game tbh. If all lanes go even, Ez winning they can litterly push you faster than you can catch up. Granted this will never happen in low ello bc players do not close out games well there.