Hello Tdog, welcome to the site.
I wonder whether the one reason is that it's different than what happens during the day because there are distractions, whether or not that's what we want, but life goes on around us, whereras at night we're all alone, so our mind is allowed (not that we particularly want it too) to ponder or perhaps mull over what's happened during the day, and with depression it's all the negative thoughts that dominate our lives.
There are no distractions, people working around us, the phone continually ringing, having to pick the kids up from school and so on, so there is no noise or activity, this allows our mind to question and debate all these negatives thoughts, because nothing will interrupt us.
Turn on your radio to a station you like, music or talk back, but music would probably be much better because then you won't have to disagree with another person who has had the chance to ring the operator and voice their opinion, which you may disagree with, because this can cause you to be worse.
For years I slept with the radio going, the song being sung took my mind off what I didn't want to think or mull over.
Best wishes.
Geoff.