Actually it's not, they are clearly better than what they did in the 1960s. As for whether it was "state of the art" that's another matter entirely. You may prefer the poorer effects of the 60s, but that doesn't make them better.
Yes, yes, that old line... There is no "clearly better" except personal preference. I can say the original effects are "better" because they don't look so glaringly out-of-place compared to the rest of the production. But it's all opinion, there is no objective standard.
Sadly an attitude has arisen that if we don't like the past we can revise it, and this goes beyond just making a new version like a remake or reboot. Now they want to redo the actual original work. In my view this revisionist attitude corrupts the context of the original work and is disrespectful of the creative efforts of many talented individuals who strived to create art and magic with next to none of the resources that exist today.
What we might call "revising," as opposed to "preservation" or "re-mastering," has nothing to do with original intent or artistic integrity. All it has to do with is getting new money from an old property. As such, it will continue as long as the numbers are right, but little should be expected of it artistically.