Question

Why don't we directly perceive the motion of the earth

Answer 1

Earth is moving at a fixed rate, and we all are  moving along with earth and that’s why we don’t feel Earth’s spin. if  the earth slow down or change it's speed we will feel.
hope it helps
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Answer 2

Earth is moving at a fixed rate, and we’re all moving along with it, and that’s why we don’t feel Earth’s spin. If Earth’s spin were suddenly to speed up or slow down, you would definitely feel it.