It's mainly down to cost. Businesses want higher profits and you aren't going to get that in a country where you have things like workers rights, a minimum wage etc. You ship or sell the business to the likes of India or China and you bypass these things. Raw materials cost more over here as well.
For example, I work for a company and we do R&D work and make synthetic diamonds. The cost of various chemical powders and other materials we need to do this is crazy over here in the UK. Go on places like AliExpress and you can get it for a fraction of the price from China. Surprisingly, their customer service is far more responsive and caring compared to companies I've used in the UK.
I don't use the sites myself but many use the likes of Temu or Shein for the same reason when buying personal goods. The majority don't think or want to think of the ethical side of things as long as they are saving money. Given the way the economy is, I honestly can't blame for just wanting to get theirs.