Thanks for the question.

Can you tell me as at why LHC has not detected Scotinos yet?

If you check on the last figure with the cluster of red points, they all lie in a regime where the scotino is quite massive. This means, that if this particle exists, its production rate is quite small (heavier a particle is, harder it is to produce it). As a consequence, we do not have today enough data to have enough scotino (still assuming they exist) to notice something weird with respect to the Standard Model background.

Is it the experimental conditions that need changing (looking from a different angle) or simply a matter (pun intended) of chance?

The conditions will change in the future when the LHC will enter its high-luminosity phase (a much larger rate of collisions). At this point, data will be accumulated much faster and we will hopefully have a better grasp on the super rare phenomena.