That's because you're building on an existing consciouness. Even if you wipe their short term memory, you still have their long term memory from before the whole sensory deprivation tank that have formed concepts such as the self, the world etc.

I see that you're seeing the training phase of GPT as the equivalent time the adult had before, but I don't think that works. Part of what makes a consciousness emerges for me is understanding your place in the world, how your actions are having consequences etc. Being nice can have people be nice to you in return, or depending on the environment, you can learn that by being insuffurable people will just give you whatever you want (cf some toddlers). GPT's training comes short of that. If you had an actual session of GPT connected to some sort of long term vector database where it can store what it learns based on conversations, to differenciate individuals and itself etc. that might give it a fighting chance to develop an equivalent of a conscience.