Why does DNA replication need to occur?

Basically, every time a cell undergoes mitosis (one kind of cell division), various enzymes work to split each DNA strand in half, and then replace the missing half on the separated strands with corresponding nucleotides, leaving you with two identical strands. When the entirety of a cell's genome is copied (along with all the organelles), the cell can split into two daughter cells.
Imagine slicing yourself down the middle and splitting yourself in half, and then using each half of you as a template to recreate the other half.
That's the biology behind it, but the bottom line is that DNA is replicated in order to reproduce itself.

DNA replication needs to occur because it ensures that each daughter cell produced during cell division receives an identical copy of the genetic information contained within the parent cell's DNA. This process is crucial for the growth, development, and reproduction of organisms, as it allows for the transmission of genetic traits from one generation to the next. Additionally, DNA replication is necessary for repairing damaged DNA and maintaining the integrity of the genetic material within cells.