
In short, the types of people who aren't bothered by morbid scenery or activities aren't mentally stable and are probably more trouble than they're worth. And Cannibals of course will be happy to eat human flesh, but that trait is taking up a slot that could go to something less situational. Those with the Bloodlust trait have no problem wearing the clothes of dead people, and get a mood boost from wearing clothes made ''from'' people, but are much more likely to start social fights. Some traits (and some beliefs in ''Ideology'') negate these morale penalties, but come with their own problems: Psychopaths are fine with death, but gain no mood boost from socialization, while keeping all the penalties from random insults from other colonists, meaning they'll eventually become an enemy with everyone around them, resulting in brawls and injuries. Alternately, you can just ignore that by selecting the Classic Mortars option when setting your storyteller.** Most colonists will take a morale penalty from seeing human corspes in the open, killing prisoners, butchering humans, cannibalism, or wearing human leather.
Either that or military vessels that have crashlanded or from larger settlements that are more industrialized, like the Empire.

TV TROPES RIMWORLD TV
On April 13, 2013, a page for Vinesauce was created on TV Tropes. Notice how it's possible to get meteorites delivering sedimentary rocks like limestone and sandstone to your planet? Considering that a "planetkiller" game over is possible, it's not implausible that these were once part of another planet that has been deliberately blown up. A group of friends was gathered around a television playing one of the GameCube.
TV TROPES RIMWORLD FULL
Worst case scenario, your colony could be full of pacifists who are incapable of dumb labor or too unhealthy to work or psychologically unstable, dooming everyone before even the first serious band of raiders come knocking. Even if some of these pawns are skilled in medicine, agriculture, construction, and combat, they may very well find themselves overworked doing what only they can do well. They are average Joes forced to land on a hostile world through some unspecified disaster, most of which are initially unsuited for their new environment due to their personalities, ailments, and professions. Your pawns are not highly skilled, well-disciplined colonists landing on a planet of their choosing.

In addition, it is possible for pawns to be chronological and even biologically older than their own parents. Some of these people are truly alone, having outlived their friends, relatives, and the rest of their support network. Given that faster-than-light travel doesn't exist in this game, most have chronological ages well into the hundreds after traveling in sleeper ships.

Every rimworld that you play on has been terraformed by some past civilization, and all of the plants are technically genetically-manipulated wonder-crops. The fact that crops grow relatively quickly (usually within a week of being planted) makes a lot more sense when you look at the lore.
