Eladrin were not a Planescape creature in 3e. They were core. They were right there in the MM. Any Planescape specific lore about them wasn't in the 3e MM. So, changing eladrin into blink elves isn't that huge of a change. You're taking a pretty minor creature that never gained any traction and repurposing it to something pretty closely related.
It was a Huge change, it's like suddenly calling gnomes, Tanar'ri, and they were not a minor creature, and they obviously did have traction as they carried over from 2nd to 3rd Ed.