Because I do. I leave things I could easily do a couple of hours earlier in the evening until bedtime and then bedtime just becomes a list of boring chores. I sit about on the sofa watching telly until I'm exhausted and then when I finally get up I have to start with locking doors, turning things off, plugging things into charge that we need for the next day, taking evening medication, brushing teeth and so on.
I'm sure when I was in my twenties I used to just party all night and collapse into bed without worrying about any of this stuff. Which is probably how I ended up needing several root canals this year 