We've had a big history in a short time recently. I don't expect we will keep everything, do you? I mean the little ships returned to private ownership, are little and generally to people from the Thames Valley who had a few bob to look after them and hand them down.
As for the reasons we don't keep them, ships such as the recent Ark Royal, Plymouth...its the way of England. They smashed up the fighting Temeraire, its always been the way of it, you know that.
Incidentally, I was never happier until I saw HMS Invincible smashed to atoms in that Turkish yard. Utterly wank ship with a higher than national average of utter mongs as officers and men (and women, allegedly).