Motives of Paizo's Fiends?

"Encorporating"?
The Daemons are the Yugoloths-- that's what they were called in 1E, and once in a long while in 2E (the term was eventually abandoned however since Demon and Daemon are simply the Latin and Greek spellings/pronunciations of the exact same word respectively, plus it confused too many people due to the 1- letter difference-- The term was resurrected by Necromancer and other 3rd party companies since "Yugoloth" is a copyrighted term.)

I have not yet gathered the courage to delve into Pathfinder, so I cannot comment on the material myself beyond what people are posting here, though as I said before, this sounds quite different from D&D canon, especially since the Yugoloths have no intention of destroying the multiverse-- the ultimate Yugoloth goal is to snuff out Chaotic and Lawful evil (and supplanting it), then finally snuffing out goodness once and for all-- the Blood War is entirely their orchestration and is a key facet of this plan (not only that, but the General of Gehenna, with the help of the Baernaloths, is the one who inadvertently created the Baatorians and the Obyriths in the first place). While there is a small amount of overlap, neither faction of 'loth is into destroying the world or killing for the sake of killing-- the 'loths of Gray Waste are into inflicting pain and disease for its own sake, while the 'loths of Gehenna are into scheming and obstructionism.

The Divs are the corrupted souls of dead genies. They also dwell in the daemon's home plane, but they're largely restricted to the unclaimed wastelands that lie outside of the realms of the Four (Horsemen) because the daemons don't just eat the souls of mortals, they'll eat other outsiders too. The daemons just as a racial goal only care about devouring mortal souls (though individual daemons and some of the Horsemen may have slightly different broader or more focused goals). More detail on the daemons in the forthcoming BotD3.

As far as daemons and yugoloths, I tried to be very conscious of having too many similar traits in motivation and action. For instance while the meladaemons are superficially jackal-headed, they're not arcanaloths. You'd never want a meladaemon serving as the fiendish social butterly representative of daemons to interact with mortals in a planar trade city like the arcanaloths often were for the 'loths.

To be honest the closest you'll get to a PS 'loth in terms of attitude and such is Tegresin the Laughing Fiend who pops up in 'The Great Beyond' and 'Classic Treasures Revisited', and a story I wrote last year for Pathfinder Chronicler. He'll slurp souls with the best of daemons, but he's -old- and he has the same cynical deity-hatred that 'loths had, but no canonical details on what he actually is or what he truly wants. He might show up in BotD3 but if so only a mention and that might or might not survive editing.

Divs want to ruin mortal lives and prolong their suffering, they are more into sustaining evil and experimenting with it like the 'loths (and Iinchoroi).