Atlantis needed to be hidden from plain sight mainly due to the many treasures that are in this incredible city. If someone had access to these treasures they would become extremely wealthy and there are also secrets within the walls of Atlantis that we cannot even mention. It would be extremely dangerous for anyone to have access to these secrets or to reveal them to the public. This is the main reason why we have kept it so hidden.
There are some people who have come close to finding it, but thankfully these have only been close calls. There is no place out there that has the same amount of wealth and secrets as the city of Atlantis. This is why it will remain hidden for much longer until the human species evolves enough to be allowed to see it and experience it. The city holds one particular secret that would change the world forever and the time for that revelation to come is still not here.