Ok, 2 things.

First off, popularity of an item does not mean it is good. For a long time, people played Twisted Fate as an adc. People played Ezreal as an apc. People used to say murumana on Ez is a troll item, now it's apparently core on blue ez. Popularity just means people think it is a good choice.

Secondly, an item win rate isn't representative of how good it is. More expensive items tend to have high win rates, because if you're winning you're more likely capable of affording such items. Ohmwrecker has a consistent >60% win rate in ranked. Does this means it's a good item? No, it has a high win rate because people buy it to finish people who try to turtle off when they're already winning.

It's not that IBG is a bad item on him, it's just that Frozen heart brings so much more for your team. It's an ok item for game modes like Dominion where you won't get much farm or into as many teamfights, but on SR Frozen Heart outshines it.