Some are as you say - you order something and never receive it. Straight up
Some are fast fashion companies which get spun up quickly with slick ads and websites, which are somehow "going out of business" even though they were registered less than 2 months ago.
Some are kickstarters for products which obviously are just clones of other products which already are ubiquitous.
A lot are drop shippers who use slick ads to sell you something they aren't even in possession of, at 2-3x the price which you could get it for if you just took the time to look elsewhere.