Because X amount of patches down the line when he's going to get nerfed again (In an actually meaningful way) he'll magically have become so unhealthy and problematic and everything they said about him previously will suddenly get reversed to explain why he's being nerfed.
That doesn't mean there aren't problems - while Zed's ability to delete squishies with a button press and some smooth moves is going to remain intact, he has so many other additional strengths that seem to push him over the edge. Given his amazing AD stats and his waveclear, should Zed be a top-tier tower-taker? Should he have amazing clean-up when his resources are depleted? While Zed's not receiving changes in this patch, we're committed to keeping LoL's favorite playmaking ninja fun to play as, and to play against
This is the quote from when they said Zed was a healthy assassin. It seems pretty clear to me that they have an idea of whats wrong with him and just aren't dropping a Super Mega Nerf Rocket on him right off the bat, because they want to see what they can fix before resorting to anything drastic.
Here is the quote about the changes from this patch
In the 5.1 notes, we mentioned Zed as a good example of what we refer to as a "Healthy Assassin" - but that doesn't come without its own set of balancing woes. To help bring Zed in line with other champions while preserving his power as a competitive option, we've looked toward his strengths outside of pure assassination - in this case, attacking his ability to split-push by lowering his attack speed.
If you actually do the math the reduction to Zed's attack speed adds up to almost 20% less attack speed at lv 18 which has a gold value of roughly 600 gold. What this mainly does is reduce the threat of him just punching you to death without using abilities and reduce his insane split pushing. These nerfs are certainly meaningful, just not in the super obvious way.
That first quote did show that Riot has some idea what is wrong with Zed.
The patch notes prove otherwise considering I haven't heard a single person complain about his attack speed.
