Kushner's lawyer attributes the omission to Jared and Ivanka collecting art for pleasure rather than business:
Mr. Kushner and Ms. Trump display their art for decorative purposes and have made only a single sale.
The White House rules on disclosing art collections are a little bit hazy, and depend on whether you intend to sell the art, or simply want to look at it. According to the Office of Government Ethics, "if the art is intended for investment purposes and is worth more than $1,000, it should be disclosed."
Trump and Kushner's collection is definitely worth more than $1,000 (works by Da Corte and Cohen are each worth about $500,000), but ethics lawyer Robert Walker told artnet that doesn't necessarily label them as "an investment." A much better indicator is whether or not the pair often buy and sell their art.