This is an unpopular opinion, but I'll post it, anyway.
Although UC folks have a higher risk of cancer, the cancer risk is small. (For comparison's sake, you probably have a greater risk of getting E. coli from a hamburger, which sickens about a quarter of the population and kills something like 5,000 people every year in the US.)
The jury is out on whether colonoscopy is even effective in detecting cancer. The latest meta-study shows zero early cancer detection benefit on right-sided cancer and about 60% cancer detection on left-sided cancer. (That's a "D" on left-sided cancer detection.) This actually leaves a lot of people with a false sense of security. Search this forum, and you will find people who thought they were cancer free ("I had a colonoscopy X-months ago.") and find out they have cancer.
Popular wisdom holds that UC folks get better colonoscopies, but that isn't often the case given that an endoscopist needs to perform one every 20 minutes to keep the churn going. A screening colonoscopy for UC should have something like 30+ biopsies. In reality, that doesn't often happen. It's still a crap-shoot.
The ASGE, which governs the practice of colonoscopy, specifically contraindicates colonoscopy "to see what's going on," thus negating any such explanation by a medical professional.
In reality, in general, the widespread use of colonoscopy is without much benefit. At worst, it introduces increased harm (in the form of the prep, procedure, sedation) and costs.
This is my two (rational) cents, sure to be roundly criticized.