I've "left" a few times (I think I've lived outside the US longer than I've lived in the US, at least after age 14), but as a US Citizen, the most egregious aspects still apply to me wherever I am. And renouncing one's citizenship is a far bigger step than leaving, or never having had it in the first place.

Also, many of the problems with the US are actually global externalities and hurt non-citizens/non-residents abroad even more than they affect US citizens or those within the US. We essentially are responsible for the global war on drugs, for instance.

It's hard to figure out what things would cause me to be so angry at the USG to renounce citizenship but not to remain in the US and use all means to try to fix the problem. e.g. if there were a genuine Hitler/Stalin/Mao-level takeover of the US, I wouldn't be content to just flee somewhere and try to avoid it; the only reason to leave would be temporarily to raise funds/forces to try to fix it. But I really don't see anything like that happening in the US -- much more likely just a long slide into comparative irrelevancy like the UK has done over the past 60-80 years.