Damn.... that graph showing Nexus Blitz playtime is really telling, it wasn't even as popular as ARAM, and it was almost dead when it was pulled.
This graph is why Riot isn't "lazy" for focusing less on other game modes. At the end of the day, we want to make things a ton of you enjoy for long periods of time. I worked on Nexus Blitz. I wanted it to succeed as much as the next person. Players voted with their time. People just don't play the vast majority of alternate modes for more than a weekend.