Scotch is pretty simple when it comes down to it.
Differences in locality make for unique elements that go into the production of the beverage. Local water, local weather conditions, local peat, distinct shapes of stills and other unusual aspects of a distillery all end up making for a single malt which has its own character, distinct from others, though sharing characteristics of its region.
Lagavulin for instance, has long had a warehouse on the seaside and during storms, breakers come in and crash up against the walls of the warehouse. Leaving barrels in this warehouse for 16 years allows for very slow diffusion of the local environment into the cask. This is one contributor to lending Lagavulin a specific flavor that is not easily emulated.