What exactly are recruiters looking for in a screen?

I have only gotten past about 2/3rds of the standard half hour phone screens by recruiters. They have usually been around the same format:

-Describe your past roles. -Why here? Why this role? -Any questions for me? (Which is always a bit tough because the recruiter is not on the team I apply for)

I have usually given the same exact answers everytime with about 2/3 pass rate. When I get rejected at this step, I have never ever gotten specifics when I ask why. So my question to the HN community is: What are recruiters looking for in non-technical intro screens? Is it simply different from company to company and I have had bad luck? Are they looking for specific buzzwords related to the role? Are there general principles that I can apply to improve?