I think the key is to use a few drops of water or use the water you’re soaking up to activate it. Like if you took a solar shower while backpacking and wanted to dry off it would activate when you started wiping yourself dry with it which would make it easier to towel with which would increase the rate at which it activates in a positive feedback loop.

If you only consider the context of the demonstration it sucks but if you consider you might have a pot/pan that has some water on it still that you’d like to dry off before putting it into your pack it would activate from that water too right? If anything the fact that they’re so thoroughly dehydrated probably means they can pick up more water than another towel of similar size and weight.