Artworks can be relatively easily sold across national borders without alerting the authorities, with the subjective nature of the value allowing prices to be easily inflated or deflated.
I have, for a long time, wondered what portion of the high-end art market consists of money laundering. Those are exactly the properties one would want for a money laundering vehicle.
The NACP said Russian oligarchs were still all too easily able to “hide and launder their money through art objects” despite the sanctions imposed on them.
No shade to the artists, but the value of paintings is not in the art itself. Art has historically always increased in price so it's an investment opportunity for most buyers. Planet Money had a pretty good episode a few years ago about private art storage.