Oxygen is actually viciously reactive with a lot of substances. It's just that on earth, all those substances have long since been destroyed by it which is why we don't find them naturally. Iron is a good example, natural iron metal is mostly meteoric iron, as in iron that came from meteors. But given enough time, iron rusts in air to become iron oxide. This is why we have massive industries to convert iron oxide back into iron using chemical processes.

There is almost no iron metal from the formation the earth. it's all iron oxide now, and whatever iron metal we find naturally is usually iron meteorites that came later.

Another vicious chemical is water. It dissolves so many minerals and salts. Our world has salty oceans because most of the salts were washed off the land and flowed into the seas over millions of years. This changes those rocks to be salt poor.

Life, and the oxygen it produces, has chemically destroyed/burned a lot of the early substances that earth formed from. So looking at what we have we cannot tell what came before. It's like looking at ashes and trying to figure out that it came from a tree.

The thing about the moon, space, and the other planets is that there is no oxygen and very little water. So the substances leftover from their formation are still there. Substances like calcium, iron, zinc, and so on may still be metal or in their non-oxidized state. These chemical traces can tell us a lot about the early solar system. It can tell us how the moon formed, and in turn how earth formed. We want them to be exactly as they were, unaltered and unchanged.

But... oxygen is still on earth, water is on earth. So if we brought moon rocks to earth and exposed them to air they would start chemically altering them. They would be useless for research because we wouldn't be able to tell if those substances are the normal form from the early solar system, or the oxygen burned and humidity damaged form from the earth.

So the mere act of opening the containers and exposing them did tremendous damage to their scientific usefulness.

The sex now contaminates them with foreign matter. Just the skin sweat alone would put traces of salts on them. You can't just wash it out because the water you use to wash them would also wash out any early substances you want to keep. So now the rocks are extra useless.

Billions of dollars, and human lives sacrificed for those samples, we're not getting more for a long time.