Why are primers required in the DNA replication process?

because of DNA polymerase activity

DNA polymerase has activity towards the 3'end of the DNA sequence already present where it keeps on adding the new nucleotide complementary to the template srand.

Thus to counter the lack of starting a new sequence is compensated by allowing primers to come and find their complentary partner and then DNA polymerase starts it work of replicating DNA by adding nucleotides to 3' end of primer sequence.