Here’s my two cents, back in the day a company known as Sears, did not sell any appliance or corded equipment without a UL Mark on it (NRTL). They did it for legal reasons. You are correct, there is no law that calls out a product needs to be approved for Safety to be sold in the USA, but there is a way, by legal means to make companies do the right things. Most companies do, others close shop and start back out under a different name, with the same product with nothing to prove the product is safe. I would rather return the product and not use them. Thanks to sites like this, DIYers may learn what they feel can be done and what to leave to a trained professional. Then there are ones that will win a Darwin Award.
When I do Field Evaluations and components don’t have a NRTL Mark or any safety mark (Notified Body), it can’t be trusted to meet Safety Requirements and gets marked as non-compliant in the report and no approval is given. Hope this helps