They aren't and weren't the majority, but in both cases international embargoes and external pressure were major factors in them losing control of their governments. Rhodesia in particular kept trying to negotiate a power sharing deal between the black majority and white minority, and the international forces backed by both the Soviet bloc AND the British commonwealth kept nixing their proposals for supposedly giving the white minority too much power, even though blacks still would've had the majority of representation in both the executive and legislative branches. The USA under Carter gave them the cold shoulder. Despite Rhodesia having a rich economy, they struggled against a universal trade embargo from day one, that only a few nations violated. After the Carnation Revolution in Portugal and South Africa agreed to embargo them in an act of feeding their friends to the alligator in hopes of being eaten last, Rhodesia lost their only sources of military supplies.The big difference is that the Afrikaners fucked up and lost the ability to rule their country. The world doesn't work with participation trophies where you get awarded a country for really deserving it. No, you need to take it away from others, usually bloodily. I don't know a lot of the history of the Afrikaners, but if they are the majority yet despite it they surrendered their autonomy then they are responsible for the state they are in.
The Rhodesians were winning the Bush War before their supply lines dried up. That wasn't due to the actions of ZANU, ZAPU, or even the Soviets or red Chinese. It was because of western liberals, the same group that refused to accept any compromise the Rhodies put forward. Of course, instead of everyone locking arms and singing Kumbaya, the final result was genocide, not just against the white minority, but of the black minority political opposition to Mugabe too.
As for South Africa, their situation went similarly except that there was no all out war and the majority political party under the apartheid government decided to opt for appeasement of the international community pretty quickly once sanctions were threatened.
Western liberals have not treated Israel remotely the same. The US gives Israel boatloads of aid and supplies, often free of charge. Any country that wants to can trade and make economic agreements with Israel. Israel is in almost the opposite situation internationally as Rhodesia was. That it's illegal for companies to boycott Israel in the US is testament to that. If they literally had to go up against the entire world, not just their home grown insurgents and hostile neighboring countries, but also full military support of their enemies by the communist bloc at its peak, and complete trade embargo by the bulk of NATO, the Israelis might find it a bit more difficult to maintain "their ability to rule their country" than it has been.