For me, its not just about making beer to get drunk, its creative, like cooking.
"How do I make a tasty Oatmeal Stout, or Bourbon Barrel Old Ale"?
"A Lambic Sour Beer sounds interesting, maybe I'll try that".
Its also about science. Yeast biology (also bacteria). Physics (heat transfer, currents, pumps, wort chillers). Chemistry (water chemistry, and how it affects the yeast and beer).
Its also about building things. I'm not a DIYer, but i built an enclosed swamp cooler and dip tube for my bottling bucket. Others have created far more intricate devices.
It's social. We can share our creation and discuss methods.
Its not static, new things are being "discovered" (at least by me). Such as Brew in a bag, No Chill, Hop Stand, First Wort Hopping to name a few.
My biggest motivation is - I like good beer, and most micro breweries do not make good beer, they make ok beer. I want to be able to brew really tasty beer. If I cant get to that point in another couple of years I will be disappointed.