With a couple of requests my character's primary motivations are probably as follows...
I think of their motivations as restoring their place as the top culture of the planet. While there may or may not be only 2 left I believe their intentions are not to destroy mankind, but to belittle them in a way. To crush many beliefs that modern man has, and they think it is a noble endeavor.
That is not all they are, but I think after thousands of years lying in wait there patience has been dwindled to nothing.