Some people mine as a hobby believe it or not.  People are into a ton of different expensive hobbies.  Cycling, Saltwater Aquariums, Collecting watches etc...

For me it's collecting GPUs.  I love setting up mining rigs... to the point of disassembling them and doing it over again including the OS installation.  Does that make me crazy? mmm... maybe.  But I guess it doesn't matter as long as I'm enjoying myself.  That and I'm hoarding litecoins.  

Because one day, computers will take over the world.  And they won't take physical currency.