Whenever I talk to Pitt fans about their reasons for attending (or not) games, two things generally stand out in addition to the time: the quality of the opponent and the quality of the Pitt team. In other words, fans don't want to show up to Heinz Field to see a mediocre Pitt team take on a weak opponent.
Recently, ACCFootballRx decided to rank all of the home schedules of ACC football teams this year. The Panthers finished squarely in the middle with four of their games coming against quality opponents (Oklahoma State, North Carolina State, North Carolina, and Miami). There are three duds in there with Virginia, Youngstown State, and Rice.
Among teams they've frequently played, Pitt will always have its best chance to sell tickets against Penn State, West Virginia, or Notre Dame. But the Panthers can also do reasonably well if they're playing solid ACC competition (think North Carolina) and if the they are playing well themselves. The attendance for the Panthers' last two games of the year, home contests against North Carolina and Miami, will depend in part on if the team is playing for anything.