People do, but it's hard to get out. There are monetary controls, so you have to break the law to get your money out. You will also end up with very little once the exchange rate and fees are covered. So you will take a huge haircut on standard of living. But the standard of living in South Africa is something of an illusion anyway with horrific crime, a corrupt and incompetent government that confiscates private property, a jobs market heavily biased against people of non-African descent (very strong affirmative action), rolling blackouts, etc. My grandparents opted to stay and they did pretty much live out their days in relative comfort in their own house - but rarely saw their children or grandchildren.
Exchange control has been somewhat relaxed compared to when I'm guessing when your parents left. It used be insanely punitive. Provided you have up to date tax clearance I think you can now take R11m out the country per year. So approx. $600k per year. So people with a higher net worth than this who are leaving will have to a take a few years to fully financially emigrate, but it used to be much more complicated and restricted. If you have a substantially larger net worth you can also negotiate with the reserve bank! Famously Mark Shuttleworth - the Ubuntu linux founder - had a series of big court cases litigating some of these rules. He sold Thawte for approx $500m(?) to Verisign while South African but then moved to the UK. It's still a very unusual thing and foreigners are often surprised that a country with western style democracy has some China-style exchange controls.
Private property rights are intact in South Africa (for now perhaps, but things are bad enough without the need for exaggeration). Also, monetary (exchange) control regulations are quite loose nowadays, and shouldn’t affect normal people trying to emigrate, but as you say, the exchange rate makes this a moot point.
Monetary controls matter for the uber wealthy. Majority of immigrants from the third world are not that wealthy, so they either cross illegally or seek asylum. If they are qualified to get work visas, that's another option. Investment visas are out of reach for the majority of immigrants.
https://en.wikipedia.org/wiki/Legality_of_cryptocurrency_by_... says Bitcoin is legal in South Africa. I believe you when you say "you have to break the law to get your money out", because you know about a million times more about South Africa than I do, but how are they preventing people from using Bitcoin to get their money out?
There are much stricter rules now, KYC on exchanges etc. But up until 2017/2018 I'd say the tax authorities weren't paying much attention and I'd be surprised if people with money who wanted to get it out didn't take advantage.
Does KYC on exchanges stop you from taking your money out of the country if you earned it legally in the first place? I'd think that the process would go like this:
1. Transfer the majority of your legally earned savings in rand, on which you have already paid taxes, from your South African bank account to a South African coin exchange, using it to buy Bitcoin, or Dai, or Ethereum, or whatever. Since this is white-market money, KYC should be no problem, right?
2. Transfer your Bitcoin (etc.) to a wallet or wallets you control, maybe with multi-signature authorization, maybe using an Electrum seed phrase, etc. Presumably this is what an exchange is for, right? Buying Bitcoin and then sending it somewhere.
3. Move to New Zealand or the Netherlands or wherever your new job is.
In 2017/2018 people could just go to a bank, or one of the many foreign exchange companies that operate in SA, and transferred their money anywhere in the world, legitimately. Exchange controls have been largely done away with for individuals.
Source: my parents are from South Africa