Did the Anunnaki leave earth after slaughtering the first humans because they found the planet dangerous and distasteful?

This statement is inaccurate and largely an assumption as an explanation for the reduction in numbers and the disappearance for a time. That was done for their own personal reasons and benefit, as they had concluded their mission here for the time being, with taking care of the fledgling group of humanoids they felt untrustworthy to see develop within their sphere of influence. So this was essentially for them an exercise in extermination of an undesirable species and nothing more. They left because they accomplished this, and then had other things to attend to. And as history proves, they returned again with another purpose in mind for the planet, and to their surprise found it had been repopulated and then picked up things from there.