Once they're established, they can decide how many PhD students to take on. And a lot of foreign students who come on J-1 visas and are sponsored by their governments are not under that pressure. A lot of them will get a position in their home country with a lot less publishing pressure than in the US.

The professor can always set his terms, and it's up to a student to have him as an advisor. In both universities I attended, there were professors who were very fussy about how much research they did and how much money they brought in (could be 0), and if a student wanted them as an advisor, they needed to understand the risks involved.