I have a few Mexican friends, who's tradition is to take their mothers maiden name as their middle name. Always thought that was cool for the Moms, but creatively restricting.
frank, also lawton. that one's an old surname they didn't want to die out, so they stuck it in my name
If you take an educated guess I am sure you would come close. What other reason can it have other than to pass down more than one traditional family names? Why would someone want to do that? That is another case
Where I live nobody passes family name this way, but some people have second name from confirmation, so it is based on religious beliefs but other that that it has no other use.