Arabs were open to other ethnicities and didn’t try to arabize them. This is apparent in Persia, Turkic countries, etc. The regions assimilating Arabic were regions which spoke Afro-Asiatic languages, from which Arabic also hails. Similar assimilation happened with Aramaic before it and Assyrian before that, even thousand of year prior to Islam.

> Arabs were open to other ethnicities and didn’t try to arabize them. This is apparent in Persia, Turkic countries, etc.

Lol tell it to the 20th century, bud. They were fine with not executing a cultural genocide only as long as they could hold it over other groups that "we brought you Islam". Once Islamic empire stops being the unifying political force, all of a sudden you get pan-Arabism: Kurds and Imazighen have their languages banned, Jews are thrown out of the country, etc.