I agree with you about the destruction of unwanted (?) supersceded airframes. Regrettably, there's just so much history and hardware that when it becomes outdated or supersceded, it's more of a liability than an asset.
What about cellular phones? If you've got a phone that's 5 years old, it's a dinosaur!! The only thing to do is upgrade. But will you think ahead about what some collector would think of your phone in prostine condition in 20 or 40 years time? Probably not.
I, as you, lament the loss of some of the most inventive and amazing aircraft ever built - all "supernumary to requirements" - but remember - while it's still on the armed forces books, it's housing, maintenance, spares storage, administrative paperwork costs are all coming oput of the taxpayers pockets - and you know what kind of hell the press would make out of that!! There just ain't enough money to go around to preserve and/or restore every interesting or significant subject out there - more's the pity.