I suspect this is related to the case of the
Sri Lankan Tamil refugees currently on Diego Garcia, who have been in the news again recently. There's about 120 of them, and they have now been there since about mid-2021, since they got wrecked or something, including women and children, and the British government would like to deport them, whether back to Sri Lanka, or to Rwanda, or basically anywhere that can disburden the government of them. As this
2022 article in the Guardian indicates, they are being held in a fenced enclosure within the military base on Diego Garcia. It is not very nice there. They were trying to sail to Canada but don't seem to have had much idea of the size of that venture.
Part of the British case for deporting them from the Chagos Islands is that they can't apply for asylum there. It's not a place where they can live. They can't just be released to fend for themselves within the archipelago, as it is not a suitable location for a long term existence. There is no infrastructure outside the military base. You can't scrape an adequate living off the local resources.
This precise point has been a key plank in the argument with the Chagossians as to why they can't reoccupy the islands. So I suspect Dave feels a need to be consistent on the point. He can't say to the Chagossians, OK you can come home now, we'll stop claiming its unlivable, while claiming that he can't release the Tamils to fend for themselves on the islands because it's unlivable.
So that's why I think these things are related. But I'm guessing.