I just want to add one angle I don't think the other comments covered well - it is obvious that nobody pushing the propaganda angle ("encouraging them to rise up") is serious because the track record is far too clear. I can't think of an instance where sanctions have ever triggered a political change and if they do then it is rarer than a country's elites changing direction due to internal political concerns. Nobody believes sanctions will cause political change in their targets. It is almost unthinkable that they would. What could that even look like? If someone has the power to threaten a country then they don't need to actually levy the sanctions to get compliance. Countries only get sanctioned if the sanctions aren't enough pressure to cause change.
The point of sanctions is to cripple the middle and lower classes, destroying a country's ability to fund a military. That actually makes it less likely for a dictatorship to get overthrown - the middle class is too poor to organise which is desirable from the West's perspective. Dictatorships are really bad at waging war effectively, they struggle to handle the complex logistics and are easier to distract and threaten.
And frankly; we're talking about something kicked off by 60s US and UK, that map in that wiki article could be mistaken for one of the British Empire. Nothing's impossible but it'll take more than a wiki article to give me confidence that sanctions were the primary political force operative here or that the apartheid system was actually the thing at issue. I would chalk it up as unusual circumstances.
The point of sanctions is to cripple the middle and lower classes, destroying a country's ability to fund a military. That actually makes it less likely for a dictatorship to get overthrown - the middle class is too poor to organise which is desirable from the West's perspective. Dictatorships are really bad at waging war effectively, they struggle to handle the complex logistics and are easier to distract and threaten.