This is about a revolution level event, not whether you think the process is working.

It provides enough of an escape valve that if enough people who want to revolt feel that way, things would chance before violence started.

You can also renounce your US citizenship which is what truly leaving permanently entails.

Renouncing one citizenship without first acquiring another is a great way to destroy your own freedom of movement and generally undermine your own quality of life. Stateless persons are usually treated according to the amount of wealth they possess. As someone not particularly rich (by Western standards) getting free of the US requires chaining yourself to a less objectionable regime. As might be expected, the countries that people want to live in have stricter immigration requirements.

The "just leave" escape valve is thus not very effective whenever the pressure builds too quickly. Besides that, the smartest and wealthiest people leave first. Anyone left behind is less able and possibly less willing to defuse the crisis.

For most people, they have significant investment in their local community, with financial, social, and reputation capital built up over many years. Abandoning that represents a huge loss, and would require a proportionally large threat to even be worth considering.

I don't expect emigration to change anything, unless some other country miraculously changes its policy to out-freedom the US, and thereby suck all of its brains out.

Renouncing your citizenship and finding citizenship in another country is still easier, safer, and cheaper than starting a revolution.

Anyone capable of organizing and running an effective revolution is capable of leaving the US with less risk & effort.

That is the point you are missing. This is about a revolution & revolutionaries, not "is this easy for anyone? is this best for everyone?"