what does darkness have to do with exercise though? that you can't run in the dark? it is actually a lot of fun.
I'm fine with doing it, but it puts lots of people off. It can be a psychological thing, a safety issue in more rural areas, or people who just don't feel comfortable running by themselves in towns or cities in the dark.
It's not just running either. There are no other sports allowed in my area right now other than elite level. We can't even have our 5 a side, not even outdoors. Lots of people don't like running either, they have bad knees or injuries etc and find it difficult. If you don't allow other forms of sport or recreation, then closing gyms literally takes away their opportunity of exercise. I have no idea who thinks this is sensible during a health crisis. Exercise is good for body and mind, and is needed more than ever.
