It just happened. I buy a little extra, just in case I make an error. I've bought a few fabrics that I thought would work, but decided I didn't like, so into the stash they went. Then I inherited fabric from my Mom and MIL. Then people started giving me fabric. Now I have more than I want. True, it's not all LQS quality fabric, but it's nice. 2015 is going to be a stash buster year. I'm going to make charity quilts, to try to get rid of some of the fabric.
For whatever reason, I cannot buy fabric just because I like it. Everything I have purchased has had an intended use, although some of it just didn't work out.