Background

X has for a very long time offered a method to control which window keyboard input is directed to called "focus follows mouse". With this method keyboard input goes to wherever the mouse pointer is positioned, which isn't necessarily the front-most window (it only needs to have a portion exposed where the pointer is). As far as I'm concerned this is far superior to the most common alternative, click-focus, in which keyboard input goes to the top window.

Rant

This rant is really about sloppy programming. Long ago, X's "focus follows mouse" mode worked beautifully. Today, most (if not all) linux distributions install with X in click-focus mode, I assume because they want it to be more familiar to migrating Windows users. This is so prevalent that many, probably most, X users today don't even know there's an alternative. Programs keep being implemented by these clueless people that modify focus behavior themselves, I believe as attempts to reduce some of the annoying implications of click-focus. Unfortunately they often do this in ways that are truly obnoxious on a system that is in focus follows mouse mode.

This means that those users that discover focus follows mouse mode will run into these badly done applications and are likely to conclude that the focus mode is at fault instead of those applications. So they'll switch back. Focus follows mouse mode is doomed to become more and more unusable as more applications attempt to improve the fundamentally inferior click-focus behaviors because good programmers are so vastly outnumbered by clueless ones.