Affiliate revenue. The same reason they recommend all the other products on their site. It's advertising disguised as product reviews. You are a sucker if you believe anything an Amazon affiliate is telling you.
All that is to say, that's quite alright with me.
I have a low-end "Victsing" model and it works just fine (as evidenced by the hygrometer next to it), and isn't hard to clean. It isn't a complicated device to make.
(I have no affiliation with the manufacturer).