If there are more than one specific thing, why not use "Blockchains" or "JVMs"?
The definite article "the" has nothing to do with uniqueness. It identifies a specific item. With "Place the book on the third step", we are indicating a specific book, and we are identifying a specific location - even though many books exist and many staircases exist containing a third step.
Ditto @EdwardBarnard, but let me add a point or maybe just restate what he said a different way.
The word "the" does not mean that the thing we are referring to is the only one of its kind in the universe. It means it is a particular instance that we have previously identified or that should be clear from context.
For example, suppose someone writes, "A cat walked onto my porch. I gave the cat a bowl of milk." Note "the cat". The use of the word "the" does not mean that this is the only cat that has ever existed in the interest of the world. It means that it is the cat that I am talking about right now, presumably the one that walked onto my porch.
Notice how the article switches from "a" in the first sentence to "the" in the second. In the first sentence, I have not previously identified the cat, so it could be any cat. It is "a cat". But now that I have identified it, for the rest of the discussion it becomes "the cat".