Because they do...
 

Is it midi controllable? I would think anything midi capable would show up there.

Is it midi controllable? I would think anything midi capable would show up there.

I'm pretty sure NI's 1176 emulation isn't MIDI-controllable. Neither are the Plug&Mix effects that I see in the synth rack. In fact, I have verified that every effect currently sold by Native Instruments in its Komplete line appears in the synth rack. 

(duplicate post)

Go into the plugins properties via plugin manager and uncheck configure as synth

Aah, but that check box is not checked in the first place.

Have you made your own plugin layouts? Maybe you're pointing to an FX layout? Or your Synths layout has accidently gotten some FX in it?

This is described in my blog post about the new plugin features in X3.
 
In X3 any plugins that advertise VST MIDI output will automatically be configured with a MIDI out port.
As a result a rack entry is created for the routing.
 
A future update will have more fine grained control over this, including the ability to turn disable the output and remove the rack entry. 

Fair enough, but when this feature results in misbehavior by some pretty ubiquitous plugins, perhaps some communication with vendors and/or blacklisting by default is warranted? And are MIDI-controllable effects all that common? Would it not make more sense to manually enable MIDI input on effects than manually disable it?