As Jams said in his post the tickets are already sold out to big Corporates and Companies who would have gifted them to their clients and senior staff. The Tennis Federation has already made their money and they cannot sell more tickets as it will create chaos. The guys who were entered without tickets are someone well known to the Organizers and they are instructed to vacate the seats if someone claim those seats with genuine tickets. The guys who got the tickets might or might not go as they got the tickets free and many of them does not want to go due to colder weather. They are not interested to offer their tickets some interested spectators also.