Because it is essentially the same model as the one Apple currently sells as it's low end MacBook Pro, only you can find it a lot cheaper.
Obviously the 2014 version is a bit faster and better all around, but the 2012 version is very similar, still has a built-in optical drive, but runs Yosemite extremely well (particularly if you have a gigabyte of RAM or more, and the spinal can take up to 16 GB).