Why do most people use very cheap skin care products?

Because they are all the same - regardless of price.  Helena Rubinstein and Estee Lauder starting cooking their goo on the kitchen stove . . . . they're all just mineral oil and lanolin (ie sheep squeezins) . . . . you want to pay $100 bucks for a little different smell?  Go right ahead, sucker.  BTW: NOTHING penetrates the skin, whether it's to make you younger or cure the uncurable.  Cosmetics, unfortunately, are very loosely regulated - the domain of hucksters peddling to the stupid.  The real talent was is marketing a cheap product for an inflated price:  are women really so stupid to think that when they pay $35 for a Lauder lipstick they'll receive a FREE gift worth $75 ???  Are there really people that dumb?  Apparently so:

FYI:  the primary heiress of the founders of l'Oreal is Francoise Bettencourt Myers - THE RICHEST WOMAN IN THE WORLD - personal fortune of $59 BILLION !!!!!  Did that money come from loading their products with precious ingredients?  btw - most of it is made in China now.

So the Lauder family must feel cheated - her real name was Esther Mentzer - but the poor family is only worth $24 BILLION.

Go rub-on some of that blue bird oil and cure your arthritis = at least the owners will have a nice feeling in their wallets.
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maybe that is all they can afford or they just don't believe all of the hype about the expensive stuff

Most of those high priced skin care products are just charging for fancy packaging, fancy names. Regular skin care products work just fine.

A better question would be why do some people pay 60-80% more for fancy packaging when the product is the same?

Because they are just as good as overpriced designer products.
With expensive branded products  you are mainly paying g for marketing and packaging. 
The ingredients are the same.

Budget & priority

You are paying for the name.. Same thing in clothes, sunglasses..

You've asked "most people" this question? How long did that take? 

I just asked everyone on the planet. "Most" of them said they don't use skin care products at all! Why do they say that?

I can justify $150 for a bottle of Yves Saint Laurent Opium perfume because it lasts a year. A jar of L'oreal or Nivea under $20 lasts a month. Last time I checked gel cream from Shiseido, it was $300. WHO PAYS $300 FOR SKIN CREAM? INSANE PEOPLE! You can get perfectly nice vegan purses from Call it Spring online for $15 to $70. Who would waste money on a Birkin?

I can tell a big difference between my Mary Kay skin care and cheap skin care.   
They are NOT all alike.
Yes some can be over priced because of the name.  
Many people can not afford a better product. Some people don’t care

There is definitely a perception that expensive skincare is always better than cheap skincare – and that simply isn’t true. You’re actually paying for marketing fluff and maybe some fancy packaging – not potency. For example, a pricey brand might amp up the cost of a product, claiming it has some super rare ingredient, but that’s not actually what’s doing the heavy lifting.

99% of the ingredients are the same. The expensive ones just claim to have some magical ingredient but they are 99% the same as the cheap ones. 

They r poor