Dhatu-vibhanga sutta question? Why consciousness not discussed as internal and external in Dhathu-vibhanga sutta?

&quot;And what is the space property? The space property may be either internal or external. What is the internal space property? Anything internal, belonging to oneself, that's space, spatial, &amp; sustained: the holes of the ears, the nostrils, the mouth, the [passage] whereby what is eaten, drunk, consumed, &amp; tasted gets swallowed, and where it collects, and whereby it is excreted from below, or anything else internal, within oneself, that's space, spatial, &amp; sustained: This is called the internal space property. Now both the internal space property &amp; the external space property are simply space property. And that should be seen as it actually is present with right discernment: 'This is not mine, this is not me, this is not my self.' When one sees it thus as it actually is present with right discernment, one becomes disenchanted with the space property and makes the space property fade from the mind.
&quot;There remains only consciousness: pure &amp; bright. What does one cognize with that consciousness? One cognizes 'pleasure.' One cognizes 'pain.' One cognizes 'neither pleasure nor pain.' In dependence on a sensory contact that is to be felt as pleasure, there arises a feeling of pleasure. When sensing a feeling of pleasure, one discerns that 'I am sensing a feeling of pleasure.' One discerns that 'With the cessation of that very sensory contact that is to be felt as pleasure, the concomitant feeling — the feeling of pleasure that has arisen in dependence on the sensory contact that is to be felt as pleasure — ceases, is stilled.' In dependence on a sensory contact that is to be felt as pain... In dependence on a sensory contact that is to be felt as neither pleasure nor pain, there arises a feeling of neither pleasure nor pain. When sensing a feeling of neither pleasure nor pain, one discerns that 'I am sensing a feeling of neither pleasure nor pain.' One discerns that 'With the cessation of that very sensory contact that is to be felt as neither pleasure nor pain, the concomitant feeling — the feeling of neither pleasure nor pain that has arisen in dependence on the sensory contact that is to be felt as neither pleasure nor pain — ceases, is stilled.'
https://www.accesstoinsight.org/tipitaka/mn/mn.140.than.html
If you look at original Pali, what they translated as "consciousness" is actually "vijnana" - (discriminative) experience. 

The point of the sutta is, as you meditatively investigate what seems to be your "I", you progressively exclude all physical elements as obviously not "I", until you are left with just experience itself. Then you investigate that experience and realize that it depends on the sensory input, which depends on attention.

When you don't pay attention to any sensory input, experience stops. What's left is called "equanimity" ("upekkha"), characterized as "luminous" or "radiant" ("pabhassara"). See Pabhassara Sutta for the canonical reference to "luminous mind".

Then Buddha explains that although this equanimity can be shaped into any other meditative state, including the formless jhanas, the meditator understands that any such state would be contrived and conditioned and therefore finite and prone to suffering.

This realization leads to letting go of desire to attain any state different from what is presently unfolding. The resulting state is pure suchness providing no basis for suffering to arise. The meditator realizes that this indeed is the culmination of the path, "the knowledge of the ending of suffering". 



So, the "experience" is not analyzed as internal and external because we are talking about meditator's own experience as he tries to find who he is by separating from everything that is conditioned and unreliable. Experience (vijnana) itself is conditioned on sensory input and is therefore unreliable, not suitable to be called "I" or to be our basis for eternal happiness. Which leaves us with nothing to rely on, nothing to stand on - and this final realization being the only unshakable truth, acceptance of which gives unconditional freedom from any mismatch of expectations, - is the very Nirvana the Buddha is leading us to.