For starters, because of freedom of association. You are free to not work for any company you like. If you feel like an employer is oppressing you, you can simply leave (unless they’re violating labor protection laws, then you can recover damages, and leave). If you feel like your government is oppressing you, you don’t have the freedom to simply stop associating with them.
Then you have the fact that the role of companies in your life is completely different to that of government. The purpose of your relationship with your employer is to exchange your labor for money. That’s it. How you live your life outside of that is completely up to you. If you can’t come to an agreement on terms of employment acceptable to both parties, then you simply don’t have to associate with them.
You also have the fact that if you have skills that employers want, then they have to compete for your labor. An oppressive employer isn’t going to have much luck acquiring such labor.
I know it sounds like a great hot-take, but the two entities play completely different roles in society, and such a comment doesn’t stand up to the most basic scrutiny.