Games organizers said 86 percent of ticket-holders showed up Saturday, 92 percent Sunday and 88 percent Monday. The gaps have been blamed mostly on officials from sports governing bodies and national Olympic committees not using their allocations of prime seats in plain sight of television cameras and photographers.
Empty seats in privileged spots angered many British people who failed in their applications to get Games tickets in public ballots.
A potential solution was offered Tuesday when the head of Britain's Olympic body called on the IOC to take more responsibility off future hosts.
The International Olympic Committee should invest hundreds of millions of dollars in centralized ticket distribution, British Olympic Association chairman Colin Moynihan said.
"It is so important to the sporting public of the host city, the host country, to get this right that this is now, I hope, recognized by the IOC as something which they should take on," Moynihan said at a news conference.
Ticket sales here are mandated to the London organizing committee (LOCOG), which pledged that 75 percent would reach British residents.
A total of 856,000 spectators attended events Saturday, including a "conservative" estimate of 500,000 on the men's cycling road race route.
It was 900,000 on Sunday, when eight men's football matches were played. An estimated 300,000 lined the women's cycling route. Monday's overall attendance was 370,000.
Spokeswoman Jackie Brock-Doyle says organizers would not publish breakdowns of each venue's attendance, which could detail those sports that struggled to lure ticket holders.
The governing body for athletics says expects track and field will "face the same problem in the Olympic Stadium," when events begin Friday.
"We will do our best. I hope we will succeed to make this stadium full and make you forget about the other ones," IAAF President Lamine Diack told reporters Tuesday. "The public seats will certainly be full."
Reacting to problems at the weekend, organizers now contact sports officials each evening to reclaim prime seats for sale online.
Brock-Doyle said 3,800 tickets, covering 30 sessions across 15 sports, were quickly sold to the British public for events on Tuesday. Buyers for events in Olympic Park, North Greenwich Arena and volleyball venue Earl's Court will also be allowed to print out their tickets at home.
Troops on downtime from Olympic security duties and pre-accredited students and teachers from local neighborhoods are also being given tickets, without compromising security plans.
The logistics challenges facing London games organizers - and "very regrettable" images of under-occupied venues - were an unfair burden, Moynihan suggested.
"It is very difficult for LOCOG suddenly to release a great number of tickets and to whom under what conditions," the former government minister said. "This is not going to change substantially in these Games."
Moynihan proposed "huge investment" from the IOC to create a ticket sales platform which could be shared by Summer and Winter Games host cities.
"We're not talking about 100 or 200 million (British) pounds. The platform will be more than that, so we are not reinventing the wheel every four years," he said.
Moynihan said the platform proposal had not been put to the IOC, but should form part of a formal debriefing of the London Olympics hosted by 2016 Summer Games host Rio de Janeiro in November.