I'm not finding that to be true at all. The manufacturers I mostly buy are Moda, Robert Kaufman's Kona, Marcus and Northcott. I haven't seen any difference. They're all nice and thick and feel soft in my hand. There's no way I could see through any of them.
If you are not experiencing the same thing, you should get in touch with the manufacturers (they all have websites with contact info) and let them know what you've observed. Perhaps they'll ask for a sample and be able to identify and fix the problem.
I'd be willing to bet that the only thing they place above making profits is keeping their customers happy. The only way they can make the profits they do is to have customers purchase their products.