They quite literally explained that they designed the machine this way. Idk how much more specific a long and deliberate scene with direct exposition can be. Again this was in the show. They cloned robot and say they designed the machine and process in a way where you would not know or remember which one you are.
Even Robot when he comes out while literally looking at the shriveled body of himself that clearly couldn’t be him says “which am I” in confusion and says why can’t I tell which one I am. Can’t be more specific than them saying we designed it this way.
The first Towelie episode is pretty funny because the whole episode they are trying to wrap the boys into some larger plot and they literally do not care.
Earth Cancelled is another just original plot episode.