James Cameron's company does have submarines and submersibles (there's a difference) that can safely take the pressure and even go the bottom of the Mariana Trench which is nearly three times deeper than the Titanic. According to this article, he's visited the wreck 33 times. The problem with OceanGate is that their vessel was insufficiently tested and uncertified, and many experts had expressed doubts about its construction.
You can already take a virtual tour of the Titanic without leaving your front room (see video below), but now that it's possible to visit in person, some rich people are always going to want to say they've actually been there. The second video shows a very detailed 1:350 model of the wreckage with an explanation of which parts survive and which bits don't.