Is my partner conscious? My dog? Actually, I don't know. I can say that I experience myself as conscious.
In our daily interactions we never ask such questions. Last week, I hired a new programmer. We checked the CV and the code challenge. We invited the candidate to see how they get around with the team etc. At no point, we asked if they're conscious.
I think our brains are machines for predicting what happens next. Therefore, a large brain makes sense because it can simulate the world more precisely and make better predictions. One mistake of this simulation is that the brain simulates us as a conscious agent who can make their own decisions and act in the world. In contrast, we are just machines who operate by the laws of quantum mechanics.
Maybe evolution set up this illusion on purpose so that we don't get depressed and kill ourselves.