One assumption people seem to be making is that sentience is a binary: either one has it or one doesn't. It's possible that there are many levels of self-awareness, some which we would recognize and some which we would not. There may be levels of sentience humans have not yet experienced, even.

For instance, ants exhibit self-aware behavior when presented with a mirror test. Does this mean ants are sentient?

https://www.npr.org/2021/08/09/1026227683/mirror-mirror-on-t...