Well, I didn't make it. :-)
pg -- in my anecdotal observation -- tends to like to use YC companies' technology where he can. It's a bit of promotion, and it saves him from doing the work himself -- while keeping HN as minimal/core-function as possible.
At the time Notifo was added, there were a bunch of threads. I think that, since that time, there's a bit of "you should be able to figure this out" involved.
What I provided was essentially a pointer to relevant search terms.
I agree, it's not the clearest thing in the world. Again, it's not my baby.
EDIT: I should add that I'm just not up to a lengthier explanation / set of instructions, right now. Old threads have some. So, I hope the bit of a reply that I could cobble together, helps.