Pit + obelisk concept is from D3, where the obelisk exists in each town and is attended by a ghostly NPC. Idk if D4 devs are going for “realism” in limiting the obelisk to one town & avoiding the ghostly attendant, but… its presence & what it does are already creepy, so it shouldn’t matter. I think the Pit was an emergency transplant to fill-in the “endgame” anyway, when it was implemented. I don’t think “realism” is a factor. I don’t think “planning” was a factor either.
When the training ground appeared in Kyovashad, I wondered why they didn’t put one in every city back then. Going to assume there isn’t a “good” reason.