Why is Steam coming out of the ground everywhere in NYC?

https://youtu.be/mAB1gesb8cQ

1:20 the largest steam system in the world, larger than the next 9 steam systems combined.

https://youtu.be/sUq5nQXczEg

5:23 steam plant supplies 3.2M people with heat, electricity, and AC

6:00 the NYC steam plant converts 125,000 gallons of water into steam every hour

9:00 if an ancient valve leaks deep underground, a street-level stack keeps danger away from public. (Assumably, cheaper to divert the steam than dig up and replace the pipe.) Eventually they assemble the machinery, parts, and labor to fix the leak.