Why was South Africa boycotted? There were and are worse regimes in some ways.

Basically the difference is that countries which aspire and claim to be democracies by virtue of that invite a special kind of criticism, one which tries to hold them to the standards they claim to accept. In addition the fact that there is significant mainstream for these countries in our society invites critics to respond to that. There is very little support for North Korea in our society, for example.