“This is dumb”: No need to be negative when something doesn’t fit your use-case. I’m happy to take feature requests into account, but the fact that this is a free plugin with no monetization means it’s not something that goes right to the top of my priority list.
“why only manual masking”: It works the way it works because it’s how I needed it to work. The original use-case for Content Mask was to drop in individual landing pages built on external tools into one page on a WordPress site, which is why it’s (currently) one page on one URL, one at a time.
If you could, can you enlighten me on what exactly you’d like to see, I can see if it’s something I can incorporate.