Here's why:

* DNA polymerase III is the main enzyme responsible for adding nucleotides to the new DNA strand during replication. It works in a 5' to 3' direction, adding complementary nucleotides to the template strand.

* On the leading strand, replication occurs continuously because the template strand runs in the 3' to 5' direction, allowing DNA polymerase III to work seamlessly.

Other enzymes involved in DNA replication:

* DNA helicase: Unwinds the double helix to expose the template strands.

* DNA primase: Synthesizes short RNA primers that provide a starting point for DNA polymerase III.

* DNA ligase: Joins the Okazaki fragments (small segments of DNA on the lagging strand) together.

* Topoisomerase: Relieves the tension caused by the unwinding of the DNA helix.

While these other enzymes are crucial, DNA polymerase III is the primary enzyme responsible for synthesizing the new DNA strand on the leading strand.