Dont think that the reason.
It happens everywhere, even in the driest corners of baja california.
But, of course, they need to improve their terrain algorithms. This popping landscapes are one of the most annoying (visual) features in the sim. As well as I understand the intention as bad I feel about the implementation.
And, as investigated by CptLucky8 here: LOD Problems - Distances revisited, the LOD model was changed in the past to the bad (imho all that subtle and quiet “optimization” happens to make the sim squeezeable into the xbox with their poor outdated specs, but, of course, that is just a unprofessional naive guess based on my observations).
That leads massively to this behaviors as an LOD of 2 now represent an “real” LOD of only 1.4 so this popping now happens much closer to you and is therefore much more noticeable.
But, as always, I would like to be taught otherwise.