Scientists list 2 reasons for the development of paired organs in humans:

Bilateral symmetry or, in other words, the symmetry of our bodies, is a trait we share with other animals, such as fish, inherited from our ancestors. This feature appeared in living organisms 500-600 million years ago. According to one of the hypotheses, paired organs allow us to move more easily and provide greater mobility for our bodies. Symmetry might also help us to support a complex central nervous system right in the body’s center.
Embryonic development occurs in the body of an embryo at an early stage of development, and at that time, there is a midline tube that connects the mouth to other orifices. Many organs develop from this tube in the form of buds. Whether the organ will be paired or not depends on whether the bud remains single or splits.

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