Certainly someone who's already developed dysplasia or cancer should be monitored.
John, it sounds like you *might* be getting better care than in the US. One of the (numerous) reasons US healthcare has poorer outcomes than most of the developed world is that we've been programmed to expect more tests and procedures than are good for us. Every test has the risk (not small) of an incorrect result. Every procedure carries a risk of an adverse event. Most people without specific risks or symptoms are much better off without regular blood tests.
To give a personal example, I had unnecessary kidney surgery because of a false-positive imaging study. The study was done for unrelated reasons. No one did anything wrong, but I sure wish I hadn't had the test!
I honestly wonder whether a healthy rectal cuff, with a UC history but no dysplasia history, might be at much lower risk of cancer than an average person's colon.