Well, it was really the only option for him to use. The size let him show off things like the shrinking keyboard for one-handed typing. It's the only large-screen device running the Snapdragon 800 SoC (with the 930 being the only other Lumia). Honestly, the 930 would be the only option, and it just wouldn't pop like the 1520 would on-stage.
The thing is barely relevant now. It wasn't highly successful. The green variant was already retired by AT&T. Its SoC is almost 2 years old (released Q2 2013). The only reason it's a high-end Windows Phone is because Microsoft completely bypassed any flagship release in 2014. Negligence is why it's relevant to the platform, and I can't help but hope MWC leads to a 1530 (and a 940, if not a 1030) that puts this thing to shame, carrying a Snapdragon 810 and its big.LITTLE octa-core setup.