They're not unable, it's just not how the laws are structured currently - regulation is always an option. Nutrition labels weren't required pre-1990[0], but then regulation made them required, so you can look at the current amount of social media regulation as a result of the United States' governance over the past 20 years.

0: https://www.ncbi.nlm.nih.gov/books/NBK209859/#_ddd00035_