Weird in the Venezuelans case, as there is no restrictions for double nationality and having only Venezuelan citizenship doesn't have many advantages. I would guess that it is because most Venezuelans living there already have an European passport due to parents/grandparent, so no need/can't get a third
If they are permanently settled in the UK surely it would be better to have British citizenship rather than that of a country they do not live in?
The nationalities listed are all very small groups in the UK. maybe they are not really permanently settled? Someone who moves somewhere for work might end up living there a decade (and in the UK that would mean getting indefinite leave to remain) and then returning.