It should be noted that in the U.S., there are really 50 individual jurisdictions. Contract law is a state matter. Some states may be better or worse at upholding non-competes. California in particular is known for disregarding non-competes.

Also, many non-competes go totally unenforced. It's rare that a suit over a non-compete is actually filed for low-level employees. In the linked article, the writer wasn't fired because her old company sued her for competing, she was fired simply because the new company found out she had signed a non-compete and presumably wanted to avoid any potential lawsuit-related shenanigans. It's also possible that the company is trying to establish a precedent for voluntary, pro-active enforcement of competitors' non-competes within the industry specifically because they know the courts are unlikely to uphold them. If all the employers just agree not to hire someone who worked at a competitor within the last 2 years, then they don't need to worry about what the court thinks (though they may have to face the DOJ in a wage-fixing scandal, like the computer animation industry has).