Most writers really don't care. I mean, look at that nonsense Robinson wrote with the Squadron Supreme. He had Atlantis built right next to a landmass, so Hyperion could uproot the city from the bottom of the ocean floor (allegedly without killing a single soul or toppling any buildings), and dash it to bits on that landmass. There is no landmass (i.e. the top of an undersea mountain) in the middle of the Atlantic sitting right above Atlantis and there never has been.
But since we haven't had a writer for Namor in almost TEN YEARS, it hasn't been that much of an issue. Almost everyone that has used Namor, and Atlantis, in the past DECADE has only used him to prop up other characters, so they don't give rat's buttocks. Why worry about the location of the city, when you are going to have Ka-Zar go down there in his loincloth and singlehandedly wipe everyone out and destroy the city -- all on one breath of air?
No, I'm not in the least bitter.
This is the big problem. Plus EASY TO GET TO. Neither of these should be true. Even today, we don't have the floor of the ocean entirely mapped, and it is extremely difficult for people to visit the ocean depths. Only THREE people have visited the bottom of the Mariana Trench: 2 scientists in 1960 and James Cameron in 2012. THREE.
http://mentalfloss.com/article/90796...est-part-ocean
I think it was in that same Sub-Mariner mini-series, that he says the worst thing that happened to Atlantis, was when it lost it's secrecy and it's myth, and that's certainly true. Now, writers treat it like making a trip to the bottom of the backyard swimming pool.