Washing out the plastic bag

One of the oddest things I've heard around recently is that some people, in an effort to be environmentally conscious, wash out and reuse plastic Ziploc bags. This kind of puzzles me. Why would one wash out plastic bags instead of just using a plastic container that's designed to be washed multiple times and will last much longer? I don't ask to mock; I'm just curious as to the motivation. I have to say that most of the time I use Ziploc bags for such purposes as storing raw meat, and I would be dubious of the likelihood of getting all the crevices clean enough for reuse.