I wouldn't be surprised if this were the case. Those early AM shows are probably a far more lucrative market for the networks than their evening news.
When I was a kid, watching the evening news was a standard part of my parent's day (and a good time to do my homework). Now, by the time 7pm rolls around, I already know the day's big events, what the market did, if any bad storms are coming, etc. I have absolutely no reason to waste an hour of my precious time watching evening news. I wonder which network will be the first to ditch the format - maybe gradually, like replacing it with a daily news magazine, like E! (and about as deep).