Why is Wasabi Expensive?

Good afternoon Steemit! So I came across this thumbnail in my Youtube feeds and I am suddenly curious.

I know something a little bit about Wasabi when I went to dine in a Japanese restaurant and I also tried some Wasabi flavored chips before but I never thought cultivation of this herb is very expensive and laborious until I have watched this clip. This answers the questions formed in mind when I have read the title. Why is it such an expensive ingredient?