I don't think there is anything to gain from the elite keeping up a lie concerning the shape of existence. What does it do if we know the earth is flat or not? Life would continue on as normal, there isn't any special power we would get.
That said, I do think its fun to entertain some ideas, and I don't think people should blame YouTube for the videos that other people post.
OK let's talk. Why would anyone need to hide on the "under side" of earth? It is far too easy already for those in power to hide in the most remote places on known territory, places that are completely inaccessible to the normal population.
The only thing I can think of would be to hide weapons testing or even a separate population, but still all of that can be done in the Arctic or in underground chambers.
It is a topic that doesn't follow the official narrative, so they're trying shame YouTube into hiding truthful content even more so than they are doing now