It’s not like it’s a dark pattern, hidden under multiple layers of disinformation and redirection. Apps have always been siloed on iOS and it has even got better as some apps can break out of the container model (PDF Viewer is a prime example). I bought an iPhone and an iPad knowing that. If it ever bugs me, I switch to Android (which, BTW, is moving to the container model). Which means Obsidian could have requested permissions for the folder to be placed somewhere else (Textastic can access random folders on the filesystem).

Even though my phone and my tablet is capable of being a general purpose device, it was not the reason I bought them. They have a specific purpose and they are filling it well. I wouldn’t buy a microwave and complain I can’t make cakes with it.