Why must dna be able to make copies of itself

If DNA never replicated, meiosis and mitosis would slowly halve the size of the genome until each cell would die

In other words it is important for DNA to double itself to account for the cells splitting during mitosis/meiosis.

DNA Replication How DNA Makes Copies of Itself. Before a cell divides, its DNA is replicated (duplicated.) Because the two strands of a DNA molecule have complementary base pairs, the nucleotide sequence of each strand automatically supplies the information needed to produce its partner