People like heroic narratives, and WWII was the last “romantic” and heroic war (if there can be such a thing).
By that I mean that you had clear good and bad guys, and they squared off and fought in the skies, on the oceans and on land, force on force like armies are “supposed to”. There were obvious, clear and worthwhile reasons to fight as well. Finally, you had all manner of spy-type clandestine business with the various Resistances and the OSS.
The bad guys were bad, and they were competent for the most part. The war wasn’t a cakewalk, and followed a somewhat literary trajectory with the almost losing and grim tenacity, then fighting back to absolute victory.
It gives military wonks the chance to read up on air, sea or land strategy and tactics, on whatever scale they choose. It gives the human interest people a lot of very clear good/bad stuff to read up on.
And, for many of us, relatives we knew well were actually involved in the war in some capacity or other. Hell, my grandmother’s still alive, and she married my grandfather in 1942 or 1943 while he was in the Army.
Contrast that with more recent wars like Vietnam, Afghanistan and the Gulf wars, where the good/bad guys are more ambiguous, and our reasons for fighting were a lot more gray than in WWII. Add to that the fact that militarily, we far outclassed our enemies, and the narrative becomes a lot less heroic and romantic, and become complex and a little painful sometimes.
It’s harder if you’re a military wonk to get behind stories of moral ambiguity framed by overwhelming military superiority versus one’s enemies, who resort to unconventional tactics (which are thought of as underhanded by many) to try and prevail.
There’s also a matter of scale- WWII was just so humongous relative to most wars before or since, that it’s not even funny. Take Gulf War I- we had maybe a half-dozen divisions in theater to fight. That’s less than the Allies used in the invasion of Sicily, which took place while the US was fighting in the Pacific, and had just got done fighting in N. Africa. Subsequent operations were even larger, and some even were going more or less concurrently in Europe, and there was an entirely separate huge scale fight vs. Japan going on at the same time. That has to do a lot for the interest in the war- it’s not 7 divisions vs. the Iraqi army, it’s 100 US plus however many other Allied divisions vs. the German and Japanese Armies.