Why did Inspiration's damage get nerfed?

So they nerfed Sorcery primary by 5 AP/3 AD, but did the same for I+S and I+D. Why? Who was abusing Inspiration of all trees? Only three champions seem to take it more often than others. Illaoi, Ezreal, and Gangplank. All three of them just take it for Kleptomancy too. There are some secondary users like Annie, Kennen, Sona, and Vladimir. But they aren't really that amazing with it. I think Swain sometimes takes it, but I haven't seen it personally yet. I think I also saw a Fiora take Kleptomancy once.

I'm just having a hard time believing Inspiration was just so widely used they had to nerf the damage as a whole. It's such a niche tree that hardly gets used as a primary. And if this was a Kleptomancy issue, I feel like they could just lower the gold gains from it. If it was an Ezreal issue, lower HIS base AD by 3. I just don't see what could warrant this. It feels more random than anything.