The reason you cannot "just" purchase "chunks" of the English coastline is because most of our coastline belongs to either local authorities or the crown estate. There is no sane business case for owning an acre of beach because a local authority will never grant planning permission to build anything worthwhile on it, so you would "own" a chunk of beach for no reason other than to inherit the burden of managing a piece of land (and who knows what that entails when councils often have very expensive shoreline protection projects to fund!). There is no financial sense in local authorities carving up beaches into chunks and selling them to Londoners for a few grand, it's a patently absurd suggestion. The reason this is a rare opportunity is the same reason it sold for so little: it's pointless, for both buyer and seller. It's not much different from owning a piece of the moon, or a square of land in Scotland so you can pretend to be a "Lord".