Elliegod damn it @sydneyfalk has fucked with my sense of the universe by pointing out that most desert islands /aren't deserts/ and that the "desert" maybe should be pronounced "de SERT" (to indicate that it's remote and uninhabited), not "DEH sert" (because it's not necessarily actually a desert)
Lord Guysbert de Fieri 
@noelle @sydneyfalk I bet it was originally "deserted island" and morphed over the years into idiom
Sydney Falk, An Oversensitive SJW TypeFrom stinkipedia:
Uninhabited islands are sometimes also called "deserted islands" or "desert islands". In the latter, the adjective "desert" connotes not desert climate conditions, but rather "desolate and sparsely occupied or unoccupied". The word "desert" has been "formerly applied more widely to any wild, uninhabited region, including forest-land", and it is this archaic meaning that appears in the phrase "desert island".
(also from it: Similarly, the term "deserted island" does not imply that the island was previously inhabited and later deserted.)
@sydneyfalk @noelle ...huh, I always assumed deserted just meant lacking in inhabitants, not an ex-inhabitant state
@InspectorCaracal @sydneyfalk I do enjoy the idea that if "desert" means "to make uninhabited" then there's a "sert" that means "to inhabit"
we have serted the fuck out of this land
it's our land
it's not your land
from that thing over there
to go fuck yourself about that thing in the other direction...and...?
something
@noelle @sydneyfalk yeah we sertled this land good
Some people have thought otherwise (I've come across one or two, at least). But technically, no.
So Sentinel Island isn't a "desert island", it's just isolated. (As are the people there.)
so it apparently was originally a *different term* that was a homophone of 'desert', apparently? or a near homophone? and then that second meaning was applied but collective language drifts and after Gilligan's Island ended nobody debated that any more on the internet from the fifties