Another thing also is that majority of your audience might be coming from a completely different timezone, and so you might be uploading during the time that they're busy or probably asleep or something.
I did notice that views did get less from 2015 to 2016 when a youtube update was implemented but that said the things above can also affected your videos
YouTube constantly changes. It mostly depends on Time, Content and Quality. For Gaming channels there are loads of em out there all playing the same game for example wich will make it tough for the smaller ones.