Not sure why. But it's annoying that WordPress still need an external plugin to deal with scheduled posts.
This great plugin exist since a couple years. Then, it's a WP bug not being fixed since a couple years. What's stopping them to fix something so simple that can be accomplished with a plugin?
I guess their thinking is: how many people really need and use scheduled posts? not everyone. Less than 10% users? Then use the plugin. Right?
All in all, this plugin should be an embeded feature of the core. Am I so wrong? Please let me know.