we're buffing many of her core items
The best part is that this is just untrue, the only item they're buffing that currently sees any usage on Illaoi is divine sunderer, all the other items see at best single digit playrates on Illaoi. If they were buffing like Sterak's Gage or something I could see why they would be hesitant to buff her but as is this is just dishonest.
Sure, but the read is that Divine Sunder is like 1-2% winrate up for top laners when bought, which is the amount they wanted to buff Illaoi by in the first place.