Cool Daddy-O

I was musing - as I sometimes do - and I wondered why is 'cool' still… well, cool. As far as I know the word cool as an expression of approval dates back to sometime around the 50s - e.g. Miles Davis' Birth of the Cool was made around the turn of the 50s. Presumably, the word was in use then. The OED's first citation of cool in this sense is, 1947 (record by Charlie Parker Quartet, Dial 1015) Cool Blues.

So, why is it sill around fifty-odd years later, and showing no signs of going away when a whole shed load of slang, argots, or whatever you want to call them have disappeared. Why is cool still around when, for example, groovy, fab, far out and so many other, presumably later, coinings have fallen out of use?

I have no big - or even, any - theory as to why it is still around. It is odd, especially when you know that teen slangs seem to form as a way of preventing older folk from knowing what the 'kids' are really up to. You would think that a word like 'cool' would, if it were still used by the teens would change its meaning, or at least fall into only ironic usage. But, as far as I can tell (which is not that far), it still seems to mean what it has always meant.