I've considered it - although the people would have to come from somewhere (there are only so many people in the crash). Maybe after you find other colony worlds with humans, you can bring them back to the main world.

Well we hear about how there are other islands with survivors (and that Sunset Haven has the most), but we never see them. Maybe after the bombing some could migrate since their homes could have been destroyed. Or even before that to join up with others.

EDIT: fixed tag

I agree with the suggestion, as to where the people are coming from, having started a fresh replay now, there is premise for finding many other people - the trader/thief proposed to build docks and get us into part of a trading network - that implies at least 3 islands which take part in it (so far, we see Sunset Heaven, then there is Pirate Bay, but they were intercepting boats going places... which also implies more people elsewhere). Then there are all those people the Mirrows turned into bandits, who keep spawning in reasonable numbers, and the Colony Ship name itself usually implies several hundred/thousand people. So I wouldn't say that the players would be surprised if new people started turning up. Truth be told, after the Event, the main island portal does look a bit lonely/vast with so few people in it.
E.g. it could be natural that, with the docks and the trade spreading the word, that new people would come in during important quality of life upgrades by the player - e.g. building the house on the main island, or getting the nuclear reactor going on Sunset Heaven / getting someone to tend the tree on the Pirate island, etc! Another possibility could be that if a player gets certain key structures on a new island, like a hut+barn+dock, then a NPC or two comes to harvest trees+berries or pretend harvest even. That might be a nice incentive for people to develop a bit other islands, and it would be a nice reward/surprise to see that happen - after all, a bit component of this is (initial) teamwork and rebuilding civilization.

PS Just had the fisherman intro for the Sunset Heaven, and he talks about this being the island with the biggest population of survivors in comparison to other islands - implying that there are many more inhabited islands out there.