Yeah, I started to write you a very long response and stopped several times, but mark hit it on the head.
The needs of metalworking are much more complex. 4th and 5th axis work is very common, and working materials vary a lot in how to approach them. This requires very good motion control, motor/spindle feedback, etc.
(it is now possible to do this on PC's, or using remote UI's to motion controllers. it was uncommon/a pain years ago)
Contrast this with wood - if you slam a carbide bit into it as a reasonable speed and angle, it does okay :)
WinCNC, by comparison to most metalworking controllers, is a *very* simple device. It has no feedback of any kind, does very simple non-differential step+direction output at a fairly low speed, etc.
(The timer card they use to do it is even EOL'd by the manufacturer :P)
This would never work for metal.
In the end, beyond that, the niceness doesn't matter enough. It's mainly because the machines and needs in woodworking are so varying.
In metalworking, they all do ATC/4th axis/etc, and so you can just count on it existing. Given this, you can actually make better interfaces - customizability is only a positive when things change all the time or everyone has very very different needs. :)
Meanwhile, on the other side, WinCNC has no nice conversational interface for toolroom usage, etc.
It's definitively *not* better for metalworking compared to the controllers i've used.