Only the MIW"s & their cohorts, can afford to taste Truffles, foie gras, & mee siam mai hum. Only mere mortals like us can afford the lowest quality shitake mushrooms, and the occasional chicken or duck liver with our kway chap, and an inexpensive Mee Siam, never with hum.
Same reason why abalone and caviar are so expensive. Limited supply, seasonal and difficult to source. Saying that I personally think all 3 are acquired tastes and way overrated. I rather spend $$$ on Kurobuta pork, Wagyu and Kobe beef instead.