Just as a prologue. I'm not sure your premise actually is correct. I'm not sure Kissinger is particularly well remembered. I expect most people might remember him as maybe a diplomat, and that would be about it. But assuming your premise is correct, I would say he might be more remembered for maybe three reasons.

First, he won a Nobel Peace Prize. Sure it's controversial; a lot of the peace prizes are. But he's the only Secretary to win one, while sitting as Secretary. Elihu Root won, one but that was after his stint as Secretary. That's the kind of thing your friends crow about, and your enemies curse over. It's kept his name far more active than might otherwise be expected.

Second, he's a career policy wonk. He kept active, started policy foundations, was used by later administrations, and wrote countless op-eds and books. That has kept his name current. Without discussing his more recent work, he was a regular critic of the Clinton administration and was always good for a quote. That kept his name in regular rotation far longer than many Secretaries of State. And that not even diving into the more recent stuff that would break sub rules on commenting on things more recent than 20 years. But he is still active as a commentator and author. It's not hard to remember a guy who's still siting there still talking. In 50 years it'll be easier to decide if he's more remembered than we might expect than it is to analyze it now.

Third, he was an active Secretary with his own agenda, policy, and philosophy. One will rarely hear of George Shultz's policies. Instead one hears of Ronald Reagan's. Kissinger ran State more on the model of a Seward. His presidents still had agendas of their own, but a lot of policies had Kissinger's name on them, not Nixon or Ford. He has generally been viewed as more of an independent agent than other Secretaries. Rightfully or wrongfully this image has kept his name current. You'll still hear people talk about Kissinger style diplomacy. One rarely hears of Albright style diplomacy. This may be also an artifact of him still being active, ala my second point. Will Kissinger style diplomacy still be a term in vogue when Kissinger is gone? It's impossible to know. So more time is likely needed before your question can be answered definitively.

For those of us in the China field, Kissinger and the entire Nixon administration is largely remembered for the "opening up" of China following the two trips Kissinger made to the PRC and the subsequent summit between Nixon, Premier Zhou Enlai, and Chariman Mao. The normalization of diplomatic ties between the US and the PRC that followed paved the way for the reentry of the mainland of China into the larger international system. Ultimately, when China experts or international relations experts discuss 20th century Chinese politics and diplomatic relations, Kissinger is almost always brought up.