I buy most 'variant covers' because I enjoy the art.
Some people will buy a variant for the same reason I did. Some people will buy it because it's a 'limited variant'. Some people will buy it in hopes of flipping it or reselling it later.
Why does everyone care how other people spend their money and for what reason. If people want to buy 'shill' items at inflated prices or if people want to create items and drive the price up, that's capitalism.
Caveat Emptor.
As a buyer you need to inform yourself on the product you're buying. I have payed WAY more for some books than I should have because I was ignorant to the market. It's part of living, learning and collecting.
Please don't think that I endorse the 'pump n dump' across multiple websites, but this is the way that any market works. In some cases, I like the marketing so I am at least aware and can buy the product before the 'pump n dumpers' buy em all up and charge triple on ebay.
Just an opinion, everyone has one!