I would guess because he didn't know. Do you know all of the business partners of any of the companies your 401-K is invested in? Do you know who the largest shareholders of those business partners are?
Is there any really good reason to expect that Ross should know 1) who the largest owners of a company that a company that Ross owns some interest in sometimes does business with and 2) the names of all of Putin's extended family?
Does your 401-K personally include a controlling stake in a large shipping company?
My pension plan has multiple stock-market investments but I'm not aware that I own a controlling stake in a multi-million pound company as a consequence.
If I later discover that my pension investments do include this, I'll concede that it was reasonable to overlook this.