If you don't understand why a subway gap is sick you kinda don't understand street skating. It's not about the fucking stair count or inches. It's about approaching something that seems impossible or unlikely and making it a spot. People love when Max Palmer does it on random ledges or those metal planter fence thingies. In this case it's the NY god damned subway- probably the most iconic mass transit system in the United States. Even if you don't skate you can see that the gap is huge, ground is often slippery or disgusting, stations are mostly crowded, and it's not easy to actually thrown down and skate. Most people couldn't tell the difference between a 14 stair and an 18 stair back lip or something, but they can definitely look at a subway gap and be like "how can you skate that?". To me it's like when people were first skating some of the spots that are described in This Old Ledge- like why would you want to launch out of the Brooklyn Banks into a highway exit? There's plenty of other banks to skate, but its the details of how sketchy and ridiculous it seems that makes it a cool spot vs just putting a trashcan at the top of a bank in a skatepark.
When spots get iconic to skaters it's often a lot of incrementally harder tricks down the same thing. I guess TJ is sorta doing that to an extent, but unlike Hubba, which was tall and had a straight run-up, having to carve around a corner on slippery ground and then set your rear foot up to scoop is sketchy AF and isn't just a "this is a hard trick", but "its not only a more difficult trick but also one that is simply harder to even setup for". And Tre flips just look cool when they're popped. Most skaters can identify Kalis' Tre flip silhouette and eventually this will be one we all know too.