Why are most turbofans tractors, but most propfans pushers?
"Most propfans" is a bit of a strong way to put it. The An-70 is the only production propfan aircraft, making the Progress D-27 the only mass-produced operational propfan. So its configuration is the norm.

As for the reasons for experimental propfans using the pusher configuration, it's generally more efficient in aircraft to begin with, as the airflow is accelerated after passing the obstruction (fuselage). In a propfan, it also avoids the need for a long LP shaft.

As for why turbofans near-universally use tractor, the main reason is that the compression provided by the fan takes part in compressing air for the core. I'm less than 100% sure that it's actually worth the extra components and drag for placing the fan forward, but the alternatives are either having a long suction duct or having a separate ring cowling for the fan, none of which are ideal.

The tractor configuration of turbofans also helps a bit with core cooling. That wouldn't apply to a propfan, which needs a cowling for the core either way.