@Luit ****************
you got beat up on the playground a lot as a kid, didn't you? You talk with a whole lot of certainty, but never provide an ounce of back up. If there is "nothing unwritten here" then show us where it is written.
The DTV, as plainly stated on the document itself, is a tourist visa. That tourist visa has a duration of 5 years, and in order to qualify for that tourist visa under the soft power category you had to take a cooking or muay thai course of at least 6 months - sometimes more and sometimes less depending on where you applied. Or undergo a course of medical treatment that was specifically delineated with a timeframe. Nothing anywhere said that continued entry via your tourist visa was contingent upon continued participation over the 5 years in cooking classes, muay thai lessons, or continuously undergoing the medical treatment you gave when you applied. With the medical treatment plan, if you told them you were getting braces and the plan was for 14 months, why in the world would they give you a visa for an extra 46 months?
It can be said that the rules and regulations regarding the DTV were poorly written. Which has given irritable immigration officials in places like Phuket the leeway to pressure people to prove they are still participating in muay thai or cooking, but that doesn't mean it was ever meant to be a requirement.