TfL have announced official names and colours for the Overground lines:
We’re giving the lines on the London Overground names that celebrate London’s wonderful and varied cultural heritage. In this blog post, we tell you all about the names, the stories behind them and when the changes will come into effect.
People call it that because “Elizabeth Line” is too long, blame them
I’m not blaming anyone; it was a reference to Mel going off about Crossrail on the Big Fat Quiz Of The Year