It’s because we have an atmosphere enabled by our magnetic field that prevents solar winds from stripping it. Your mass has much more pressure applied to it inside of it. That combined with the continuous spin of the earth on it’s axis, as well as, it’s orbit around the sun all produce gravitational forces that prevent you from “falling out” into space or perceiving an “upside down” orientation.
I can confirm through personal experience that this is true.
I have been to the southern tip of New Zealand, which if you look at the globe, is way down at the bottom. Surely, anyone standing there would be aware that the are obviously upside down?
But nay! Despite my fears, I had not the slightest feeling of being inverted. And I never saw anyone fal off the earth the whole time I was there.