In 19.10, Kubuntu, Lubuntu, Ubuntu Mate and Xubuntu all have the ability to make a window occupy the upper half or the lower half of the screen using Meta+Up and Meta+Down respectively. But Ubuntu 19.10, out of the box, doesn't: instead, Meta+Up and Meta+Down maximize and restore windows.
Why is that?
One possible reason is mentioned in Analyzing GNOME keyboard shortcuts which is one in a series "to analyze keyboard shortcuts in most major DEs". Quoting from there:
Meta+arrow does not match a full set of tiling like Plasma (in which Meta+Up/Down tiles up and down), that is, it does not match semantically, because GNOME acknowledges that tiling up and down is a waste of vertical space; instead, the more commonly-used maximize+restore is default.
The next paragraph in the article provides further argumentation citing linguistics and "how Up for maximize and Down for restore feel intuitive".
I briefly search for any official GNOME documentation justifying the use of Meta+Up and Meta+Down to maximize and restore windows respectively but couldn't find any. This classifies these shortcuts as "System reserved shortcuts" but doesn't provide any reasoning.