Don’t get me wrong – I’m not claiming migration is the only thing that can make governments improve. In case of China there were certainly other reasons (though the successful examples of emigrant Chinese in Taiwan, Hong Kong and Singapore may have played an important part).

couldn't we say the same thing about voting?

There are several important differences.

1) When you choose to emigrate (or switch to Netflix) you make a personal choice and do not force other people to follow. 2) Emigrating would directly affect your life, so you are likely to consider it seriously. Voting does not (one vote never decided a major election), so you are free to make a purely emotional choice.

When I left cable for Netflix... I left one bundle of content for another bundle of content.

Imagine what would happen if only one cable company was allowed to operate in each country (just like the government). Regardless of how accurate is their information regarding your preferences, it is virtually certain that their services would deteriorate. This is an inevitable consequence of a monopoly system.