What happened to these professors after PhD

I am a computer science student from Turkey. While I was checking the websites and publications of various CS Professors in Turkey for my future studies, I noticed a strange trend. (Excluding minor exceptions)

Usually, these professors hold a Ph.D from leading western institutions, and during their Ph.D they have published papers at extremely competitive top venues, like ICCV, ICDM, ICML and other places depending on their research interests. But, after returning back to Turkey and starting in an academic position, they can't even get their papers published in second tier venues.

So, what might be the reason for this ? If these people can publish during their Ph.D then why can't they do now ? Also, CS is not a field where extremely expensive lab equipment is required. So why are these people unsuccesful at publishing in top conferences/journals ?