Also, evacuating the crew of a hostile vessel must be an incredibly complex operation. Even though Picard had just witnessed that transporters worked for him, he should have had no reason to think that they would work for the Romulans, for the required time, at the required efficiency; even in ideal conditions, the task might be flat out impossible (compare with the timetable in "11001001").
Plus, let's not forget that Picard's motivations for keeping his Romulan captive alive in "The Enemy" were not altruistic. The Romulan was being held as a pawn, and his death would have made Picard look bad in addition to costing him his one ace in the sleeve, the potential and potent threat of him being able to interrogate a confession out of the captive. Picard really isn't the sort of a skipper to turn the other cheek.