I've sprouted a few things (tomatoes, pinto beans, carrots) in plastic
bags on a wet paper towel. If they go dry for just a day they more or
less die.

The plants I've sprouted outside in the ground from seed are FAR more
hardy. They're significantly more green, and can go for several days
without watering.

Do you think this is a matter of lack of sunlight, too much water, or
both?