CAN SUNNI ARABS FIGHT SUNNI ARABS?

We see situations that call for Arab Sunni Tribes to fight Arab Sunni tribes, but it rarely occurs no matter how awful the Arab Sunni Tribe may be (e.g ISIS though ISIS may take over them).  There was a period in the Second Iraq War where some Arab Sunni Tribes did fight the Sunni insurgents I believe but were handsomely paid to do so.  However, in Syria, we seem to be able to get many Arab Sunni recruits to fight  Bashar al-Assad (who is not Sunni) but have great difficulty getting any Arab Sunnis to fight ISIS, even though many of the ISIS fighters are foreigners.  Yes the Kurds will fight ISIS with gusto, and they are Sunnis but not Arab Sunnis.