When Lovecraft wrote his stories in the 1920s and 1930s the world still seemed to be full of hidden, unexplored places. Hidden cities and lands forgotten by time seemed possible. Now, in 2017? The world is mapped. Maybe not completely but with enough detail that any current Cthulhu Mythos authors have to work harder to explain how a place manages to stay undetected. “The government is covering it up” might work for something relatively small that exists within the borders of that country but how would “they” cover up the existence of an entire city (much less a range of mountains taller than the Himalayas) on a continent that is owned by no one? That would require a lot of cooperation between governments and a lot of people who are willing to be silent about that cooperation.
Some authors suggest that the Mythos entities hide from us. That seems unlikely. They can travel between the stars. Some of them can travel between the places between the places between the stars. We can’t be a threat. So if they’re hiding, perhaps they’re hiding from each other. Or from something even bigger and scarier.