Why don't we get dizzy from the earth's spinning?

Shut the heck up. Now.

We do not feel any of this motion because these speeds are constant. The spinning and orbital speeds of Earth stay the same so we do not feel any acceleration or deceleration. You can only feel motion if your speed changes.

Sit in a chair which can rotate and go around once in 24 hours and tell me how dizzy you get.  Btw that is an RPM of about 0.000694.

If you are thinking of spinning like what a figure skater does, someone standing at the equator doesn't spin at all. The rotational component on someone standing upright increases towards the poles, but there is one spin in 24 hours.  Do you think you would get dizzy spinning once around in 24 hours?

It is like being in a car that is travelling at a constant speed on a smooth surface. You feel no motion. We only feel changes in speed which are called acceleration. Because the Earth rotates at a constant speed you do not notice it.

Our sensory system is only tuned to noting changes in acceleration and there is none when it comes to the rotation of the earth.  Most of what we detect via our senses involves changes.  We don't notice or pay attention to sameness.  We are not built to notice it.  Sameness is not a threat and provides no useful information.  You might even experience induced "blindness" from staring non-stop at a specific object (if you can keep your eyes perfectly still, which is very difficult), and you certainly do not notice all that background noise that you are exposed to all the time, or notice the taste of your mouth when it doesn't change, or the smell of a room that hasn't changed.

We do not feel any of this motion because these speeds are constant. The spinning and orbital speeds of Earth stay the same so we do not feel any acceleration or deceleration. You can only feel motion if your speed changes.

I think it might have to do with the gravitational field

Because we're spinning right along with it. It's all relative, like Einstein said.

Get a protractor marked out in degrees. Stand in one place. Have a helper call out each time a minute passes.  For each minute, rotate your body 1/4 of one degree. It doesn't matter if you turn to the left or right. After 5 or 10 minutes, do you expect to be dizzy from all the fast turning?