You're correct that France did sell weapons to Israel during the Cold War. It would be incorrect to say that it was alone in doing so to Israel. After all, the Cold War was still raging in 1968, when France stopped supplying Israel with weapons following the 1967 war, and the US sold Phantom jets (F-4s) to Israel.

This was the first sale of US military equipment to Israel, or at least advanced military equipment. The US had sold defensive weaponry to Israel prior, like radar equipment in 1960 and Hawk anti-aircraft missiles in 1962. But the F-4s were significant offensive weaponry. The US, until that point, had viewed arming Israel to be pointless. While Israel was seen as quite strong, the US wanted to maintain good relations with Arab states, was still pursuing a policy of seeking them as allies (even though that ship had sailed long before, as long before as Eisenhower with Egypt, for example), and believed eventually Israel would be defeated by the sheer superior numbers of the Arab world. There was likely a level of inertia in policymaking as well that brought this about. But after Israel's decisive victory in 1967, and the beginnings of a very clear nuclear program, as well as the prospect of losing what was increasingly being seen as an ally by the US government and populace once France ceased its supply, the US shifted gears. I'm unfamiliar with relationships between France and South Africa, but France was not Israel's only supplier of weapons during ~20 years before the US began selling weapons to Israel. In fact, the Soviets (through Czechoslovakia) had sold Israel some frankly pivotal weapons, not of an advanced nature but much needed ammunition, rifles, etc., during the course of the 1948 war. However, no other country was a major arms supplier during this time; it's not like there were many to choose from, either, if the US was unwilling. The Soviets were certainly no friends of Israel; an early relationship was ended with the antisemitism rife in Stalin's Doctor's Plot and the general sense that Israel would align with the West after all, and was no longer useful as a wedge to harm the British once established. Still, if we already know why the US was reluctant and the Soviets hostile, why the French and not the British as the next runner-up? The British were already supplying Arab states, and had been since the 1948 war, expecting (and perhaps hoping for) the Arabs to win. In part, this supply was meant to mollify Egypt as the British were debating and arguing with them over bases still present there. The increasing double standard was argued against by Israel, but the Foreign Office refused to reconsider, perhaps still hoping to influence Egypt and otherwise not caring much about what followed. Some internal voices laid out arguments that selling arms to the Arab states but not Israel was more likely to lead to a war, but these were rejected or ignored. But when Czechoslovakia (i.e. the Soviets) sold weapons to Egypt, largely mooting any influence the British might have had, the British did not reconsider. They kept supplying weapons to Iraq and Jordan under preexisting treaties. They also sold 20 tanks to Israel, but not heavy tanks and certainly not a significant bolstering of Israeli forces. The Foreign Office figured that if Israel was attacked, it could survive without British arms, and that if it couldn't, no amount of arms would suffice to defend it. The British also stuck to a desire to implement "Operation Alpha", a peace plan they hoped to carry out between Israel and the Arab states that never got off the ground; arms provisions were a major carrot/stick inducement to try and implement it. The British in 1956 were asked once more to sell the heavy tanks, even secretly, but refused saying that such a sale might deter Egypt, but would damage their relationships with Iraq and Jordan, and so they declined. The UK did, around 1958 following the collapse of its Middle East policy, start to sell those heavy tanks to Israel. So while the UK and the US were willing to sell to Israel eventually, it took time in their own respects to reach that decision, largely because of their own alliances with other states (i.e. Israel's enemies) more than anything else.

The relationship Israel built with France, however, was stronger. In large part, it began because France held sympathy for Israel. France was fighting in Algeria, and Nasser (Egypt's leader) was helping supply the Algerian cause. Israel was obviously opposed to Nasser, which meant the two were naturally aligned. France lacked any such good relationship with Egypt or hope to sway it that the UK had, and lacked a relationship with Iraq or Jordan, and its existing relationships with other Arab states were not as strong at any rate. There was also a good commercial component to it, which certainly did not hurt.

France would eventually switch to ending sales to Israel after the 1967 war. This was in part because the alignment of interests had shifted; France had withdrawn from Algeria and no longer had the same opposition to Arab nationalism at play. Additionally, some nasty antisemitism came to the fore on the part of Charles de Gaulle, who called Jews "an elite people, sure of itself, and dominating". This was jarring, considering his prior support for Israel. Books, letters, and compendiums all show his complex views on Jews. Some posit that his comment was merely because he was upset with Israel having launched its preemptive strike on Egypt, which he had opposed; still, that seems like poor excuse for antisemitism, and is unjustified by any measure. He certainly faced significant opposition within France, and that antisemitic comment led to a furor. Nevertheless, France decided to try and court the Arab world after 1967, rather than stay aligned with Israel, even as the US was doing the opposite.

I'm not sure, but I don't know that there are parallels between France-Israel policy and that of France and South Africa, or of the world's and South Africa's. I imagine the two are different in terms of France's motivations, and the world's motivations, but plead unfamiliarity with South Africa overall.