Why do people Rush Morellonomicon on Ekko? Is Luden's a better rush?

Ekko runs out of mana pretty quickly and he's basically useless without mana. Morellonomicon is a common rush item for Ekko in Mid or Top lane. Also, the CDR is nice and his ultimate is up more often.

In the jungle, he's fine since he gets the blue buff and the runeglaive enchantment helps his sustain a bit.