AI doesn't accept free settlement?

[K-Dogs]

So in my current Casse campaign, at around 260ish BC, I'm campaigning in Iberia and have taken most of the territories there (I figured instead of having to rush into Gaul with a few stacks and be surrounded by new enemies, it'd be more sensible to take a little longer and take on the slow-starting lusotannans, capture the whole of iberia and have 2 pretty much impenetrable powerhouses, Britain and Iberia, to fuel the rest of the campaign), and had to force diplomacy an almost dead Lusotanna into becoming a protectorate.
Also having taken Darioritum (Northwest Gaul) and Burdigala, I decided to try and give them a chance to migrate and tried gifting Darioritum to the Lusos, but got the old 'We can provide nothing in return' answer from their FM. I tried Force Diplomacying it, didn't work, and neither did offering other nice gifty things too.
I tried giving Burdigala to the struggling Arverni but got the same result.

Is there any reason why the AI keeps refusing to accept my offers?

[MarcusAureliusAntoninus]

If you give them a few thousand plus the settlement, they'll usually take it.
Or, if using FD, try asking for 1 mnai in exchange for the settlement. FD does not work unless there is something on both sides.

[Irishmafia2020]

If you give them a few thousand plus the settlement, they'll usually take it.
Or, if using FD, try asking for 1 mnai in exchange for the settlement. FD does not work unless there is something on both sides.

This statement is accurate, however asking for map information in exchange for a settlement works as well as 1 Mnai...

[Chris1959]

Darioritum is a long way from the Luso, so they now it might revolt you may have to give them a hefty sum of cash to sweeten the deal, or use force diplomacy it's the best way if you intend to manipulate other factions.
Sometimes the AI kinda knows they won't be able to hold a settlement they are not joined to, I once saw Emporion revolt to the KH who gave it to my enemy the Luso, a few times I would take it and give it back to the KH and they would then hand it over again in a ceasefire

[Jebivjetar]

I usually offer 5000 mnai + settlement and AI never refuse the deal. Doing that as Epeiros i've helped Saba to build it's own empire.

[K-Dogs]

Ah ok, I'll have another go in a sec. hopefully I'll be able to completely displace the Lusos, to somewhere where they can eat at some bigger factions, but I'm sure it won't go to plan, and that's what i love about EB