Rather than making sweeping statements as to why the eldar don't currently use robots, perhaps it is more reasonable to look at the 'history' of the 40k 'fluff'. The "Torturer's Tale" indicates that at one time (pre-Fall) they did use artificial constructions. These were 'robots' in much the same way as we think of them, perhaps even shading towards Von Neumann machines which might reasonably have been in their technological grasp.
Then came the Fall. We understand that 'Seers' foresaw the Fall, one of the reasons for - some argue - the construction of new craftworlds as well as the increased exodus out of the core empire... Slaanesh is born but, at this time, do they have an analogue for the Infinity Circuit up and running? (Something I still see as being based on the more 'primitive' World Spirit.) Perhaps not. Perhaps the
Tuisich Novasmair were an intermediate period, one where the 'soul' must have been directly grafted into a machine before life departed... these broken, once dead warriors were truly 'Phoenix Warriors' (rather than the Phoenix Lords!
) It is not certain whether the eldar still operate significant quantities of autonomous robots, since if they were that important to society (i.e. leading to the hedonomis) then the 'blue prints' (to use an obvious, if misleading, term) in the pre-Fall period it is possible that they would have been used in the interim period between peri-Fall and post-Fall craftworld society.
Eventually post-Fall society matures and the Infinity Circuit - and hence the Eternal Matrix - is developed. The basic premise of the
Failleanam is extended to the Waystones, etc. Perhaps even some of the
Tuisich Novasmair could be recovered from their eternal prison... Indeed, using this model one could wonder whether it still might be used.
Anyway, the C'tan and the Necrons once again arise. Kind of like robots, are they not. Perhaps there is a global spread of distrust of the 'machine' and a shift away because of problems with them... Were they vulnerable to TEMPEST hacking or the equivalent?
Just a thought, since I prefer to integrate all the 'fluff' rather than just take the latest revision!
Kage