>>532012920
Why and how would they ever find common ground? They're both hyper racial supremacists that believe their people are destined to rule the galaxy. There can be only one, basically, at best the Eldar and Imperium would ally to kill everyone else first, than turn on each other in full genocidal force. And since both of them are aware of that, no real alliance is possible since they would both be looking to betray and screw over the other one the moment it was opportune and advantageous to do so. Peace and cooperation is not and never was a a real option.