Nope, you’re just oblivious to Thai culture. Doesn’t matter what you solipsistically perceive to be erroneous or ridiculous about thi culture, it just is.
By returning the trash bags, you’re (1) suggesting that something is faulty, (2) making them do extra things they may not know how to do, (3) making them do things they may not be permitted to do.
unless it was something expensive and genuinely faulty, I’d just let it go and keep the trash bags.