Most people wouldn't die from UC if they never took medication. It's only the severe cases which get to the point of being life-threatening. And even then, most people with fulminant (life-threatening) UC would still live long enough to procreate and pass on their genes first. Ditto those with Crohn's.
My Crohn's came from the Irish side of my family. I never knew how poor they were prior to Ireland joining the EU until my mum told me about
her experiences on their farm as a child: no electricity, no running water (it came from a well), and a diet consisting largely of boiled potatoes, bacon, cabbage, eggs, milk and cream. So yeah, these were deeply poor, rural folks who somehow developed a pr
opensity for Crohn's.
Crohn's at least (don't know about
UC) may even go back to pre-neanderthal man. /ibdnewstoday.com/2015/02/02/new-study-finds-genetic-features-associated-with-crohns-disease-psoriasis-date-back-to-pre-neanderthals/
PS: I'm not recommending going without medication. Decades of living with an inflamed colon is neither healthy or fun, and increases the risk of colon cancer - dramatically so after a few decades.