Why is J1 dominant in Arabs?

[Opie]

If earliest Semites are Natufian which is associated with E haplogroup, why is J1 dominant in Arabic countries of Middle East.

[ShieldWolf]

Origin and diffusion of human Y chromosome haplogroup J1-M267

The theory is that they were successful goat herders from Eastern Anatolia and the Zagros mountains that migrated south into the Levant, Arabian peninsula, and North Africa.

[chinshen]

If earliest Semites are Natufian which is associated with E haplogroup, why is J1 dominant in Arabic countries of Middle East.

Because being Semitic is just a linguistic and not related to DNA.
It has been historically recorded that during certain circumstances some ethnic groups changed their language family, but of course they could not change their DNA and also due to admixture overtime would have an effect too.