It is marketing and PR. His country is at war, a suit would give the optics of a politician -- which he 100% is-- but he does not want to give that impression. It might remind people of how corrupt Ukraine is or was, as per the USA's own news media reporting on him, and the country, pre-2022. This sells it better for people who do not study or know of the region's history of the last 30 years.
Philosophy. Biology. Statistics. Research. Skeptic. Sometimes Photography