A few reasons:
1. Because I f*u*k*n* love the smell of mashing grains in the air and fresh hops right out of the Mylar.
2. It gives me an excuse to drink beer and do something seemingly productive at the same time.
3. I enjoy making, creating, and innovating equipment used to make beer which provides an opportunity to combine pure geek (engineering) with something quite cool (beer).
4. My garage looks like it belongs to a mad scientist, filled with metal canisters, conical vessels, pots with gauges, beakers, flasks, stainless steel tables, etc. It's fun to freak people out by showing them, especially if they have no idea how technical making beer can get.
5. I always have something to say if asked "what's one interesting fact about yourself".
6. Kumquat Kolsch? Oyster Stout? Imperial Indian Stout Ale? Those cannot be readily bought at most bottle shops but you sure as hell can brew them yourself (and they are wayyyy more delicious than they sound.
7. It sure as f**k beats stamp collecting.