Why does nobody ever build Luden's Echo on Ekko?

I feel like Luden's is an incredibly underrated item on Ekko. To me it makes him a lot more bursty than he would be with Protobelt simply because of the passive alone. Also, buying a Lost Chapter early on is actually super good for him as he does lose quite a lot of mana in the lane phase, and even later on, so having that extra mana is a huge bonus for him.

Usually my full build on Ekko looks something like (some items are interchangeable depending on the circumstances of the game) and I get a lot of success with it because he tends to kill enemies so quickly that they can't even react. Now I'm not saying that I think Protobelt is a crap item on him, because if Ekko falls behind the reliable damage from Protobelt can be super helpful. But what I'm saying is that people tend to build Ekko and Fizz pretty much the exact same way which confuses me because yes, Fizz is also a melee AP assassin but his kit is more build to one-shot enemies, while Ekko's isn't really like that. So building Luden's on Ekko for me helps him to burst multiple enemies a lot more quickly than Protobelt does.