This is too simplified a position:
1. A company can usually go without hiring people than a worker can go without making mortgage payments or issuing rent. In the United States, that includes basic access to medical care.
2. Companies have large legal departments advising them on how to craft language and the boundaries of the law. Most workers don’t even want to pay a lawyer to review a contract knowing that they’ll almost always be told it’s standard and there are no exceptions.
3. People join a company when the relationship is good, and aren’t thinking about how it could be sour. This often includes verbal assurances about things like this which are not written into contracts, and a change in management which provides reason to leave also invalidates all of your assumption about who you entered into the agreement with. If you signed with “only a direct competitor” that probably seemed more reasonable at the time than when the new boss / acquiring company decides that since you work on software anyone else who works on software is a competitor. A lot of open source developers went through this with IP grabs which were agreed to cover only their new employer’s direct business but then a change in ownership meant that someone was trying to claim their hobby game or even non-software IP.
Yes, ideally everyone would know about this and refuse to deal with abusive companies but the reason we have laws is because that’s not how the works has ever worked. Providing clear boundaries is useful both because because society is healthier if even people who make minor mistakes or trust the wrong person are protected and because it levels the field for everyone. If the law says no non-competes, people don’t need to generate millions in revenue for lawyers telling them why company A is offering less than company B, and company C is not going to try to bully their existing employees into accepting a worse deal. It’s the same reason we say “your boss can’t demand sex” / “teachers can’t have sex with students” because that avoids having to individually litigate each case to decide whether some power gradient was crossed. Simple boundaries are enormously useful, and in this case there’s really no downside (New York would love it if banning non-competes devastated their economy into California’s).