Comment by ChuckMcM

I friend suggested that often fine art is "on loan" to museums from some rich person's estate and that having it 'stolen' allows the estate to collect the value of the insurance claim rather than taking the painting back and selling it on the market (which may or may not return the value of the insurance). Also it probably looks bad if "The Frobotz estate has asked for this painting to be returned so they can sell it."

Turns an otherwise illiquid asset into cash that the estate could use.