First of all, it's not now. Not this late in the evening when I'm tired. And not that alone. It's also due to having all the things I have come across the day that is in my mind. It's hard to pick a topic from all those things running through my head after a day. Everything that has happened, all the things I have read about and so on. That's quite a lot of information.
It's not easy to write first thing in the morning either. You are still half asleep. That just doesn't work. You need to be well awake to be able to write anything. But after a night of sleep at least most of the noise in my head is quieted, refined to its core and pruned from the useless info.
So I need to give it a while. Wake up properly and be ready for it. It's also good to get some light exercise and fresh air before starting. Just enough to find the clarity, but not yet cluttering my mind with too much information.
So, empirically for me, the perfect time for writing is around one hour and twenty minutes after waking up. At least then it feels easiest to do. And I think I have written some of my best posts around that time.