Monarch chief executive Andrew Swaffield has said he is “absolutely devastated” at the airline’s collapse.
Mr Swaffield said the decision not to continue trading was made on Saturday night after estimating that losses for 2018 would be “well over £100m”.
He told the BBC’s Today programme that Monday was a “heartbreaking day”.
Meanwhile, the first stage of the Civil Aviation Authority (CAA) rescue scheme led to nearly 12,000 people being brought back to the UK on Monday.
A similar number of people are due to return to the UK on Tuesday.
Monarch Airlines ceased trading early on Monday, leading to nearly 1,900 job losses and the cancellation of all its flights and holidays.
The collapse of the 50-year old company is the largest ever for a UK airline.
Mr Swaffield blamed the company’s demise on “terrorism and the closure of some markets like Turkey, Tunisia and Egypt,” which led to more competition on routes to Spain and Portugal.
“Flights were being squeezed into a smaller number of destinations and a 25% reduction in ticket prices on our routes created a massive economic challenge for our short-haul network,” he told the BBC.
- What are your rights?
- The rise and fall of Monarch
- ‘Shock and anger’ among passengers
- Four reasons why Monarch failed
He explained that it was impossible for the airline to keep on flying beyond the weekend once the decision to close had been taken.
“The UK insolvency framework doesn’t allow airlines to continue flying unlike in Germany and Italy, where we see that Air Berlin and Alitalia continued when they were in administration.
“We tried to operate a normal schedule all day Sunday so we could be ready for the CAA rescue flights on Monday morning without causing a massive backlog.”
Mr Swaffield said the staff at Monarch had been a “great family” and said every effort was being made to find new employment for the 2,000 people who had lost their jobs.
“We are doing all we can,” he said. “We are talking to our competitor airlines, trying to organise job fairs and trying to connect staff with our competitors.
“We also have hundreds of head office staff in Luton and are trying to organise the same kind of conversations with employers in Luton and Bromley.”
CAA chair Dame Deirdre Hutton told the BBC that their programme to return holidaymakers to the UK had got off to a good start.
“Day one went really well and day two is going well so far but it is a huge undertaking and I’m sure there will be some glitches on the way,” she said.
She added that the programme would run until Sunday 15 October and that if people were not flown into their departure airport, they would be taken there by bus.
Dame Deirdre denied that the collapse of Monarch and cancellation of some winter flights by Ryanair meant that the airline industry was in trouble.
“The industry is very buoyant and during this year passenger numbers have been up, airlines have been doing very well and airports have been reporting record numbers of passengers,” she said.
The government is set to pick up the tab for flying Monarch passengers home, but is talking to credit card companies about sharing some of the cost.