Due to two things:

1. The fact that our washer and dryer are actually out in our garage.

And,

2. We live in a very hot and humid area, which accelerates mold and mildew.

We just don't start loads that will be unattended, even for a few hours. Because laundry left in the washer for even as little as an additional 45 minutes will need, at a minimum, to be rewashed, or possibly even just completely thrown out, as our clothes would have begun to get very mildewed indeed.