Richard Quest is CNN's aviation correspondent and author of " The Vanishing of Flight MH370 ," a new book that examines the flight's disappearance, two years on. The opinions in this commentary are his.

For most of this time the searchers have been exploring a deep, 120,000-square-kilometer stretch of water in the southern Indian Ocean.

The choice of location was based on satellite data (the so-called Inmarsat handshakes) as the area most likely to contain the missing aircraft.

However, despite finding dormant sea volcanoes, previously uncharted shipwrecks and a miscellany of sea junk, the missing Boeing 777 was not found.

On Tuesday, the search was suspended by the three governments involved.

Huge search

The search operation has been among the most challenging ever undertaken.

The ships involved patrolled for around six weeks at a time in the middle of nowhere in some of the most atrocious weather conditions on Earth, with vicious winds and huge waves. There have frequently been days when searching had to be halted because of the weather.

Even though the ships have a doctor on board, there have also been medical emergencies that required urgent returns to base in Australia.

During the search, parts of the plane (some determined as certainly being from MH370, others "almost certain") have washed up on the coasts of various east African countries. These finds didn't tell us much about how the aircraft went down, or what condition it was in, but were the first pieces of hard evidence that proved MH370 had crashed.

Photos: MH370 debris Malaysia Airlines flight 370 disappeared on March 8, 2014. As of October 2016, authorities have definitively linked three pieces of debris to the plane, while four other pieces are believed to "almost certainly" come from the missing aircraft. A flaperon from a Boeing 777 was found on Reunion Island in the Indian Ocean in July 2015. Authorities later confirmed the debris came from MH370. Hide Caption 1 of 7 Photos: MH370 debris Two pieces of debris were found in Mozambique, in December 2015 and February 2016. The Australian Transport Safety Bureau (ATSB) said both pieces "almost certainly" came from the missing plane. Hide Caption 2 of 7 Photos: MH370 debris An examination of stenciling and other identifiable features were used to link the debris to MH370. Hide Caption 3 of 7 Photos: MH370 debris Two more pieces of debris, found in March 2016, were also deemed to have "almost certainly" come from MH370, according to the ATSB. Hide Caption 4 of 7 Photos: MH370 debris One piece is believed to be from the plane's Rolls Royce engine, while the other matched a Boeing 777 interior closet panel. Hide Caption 5 of 7 Photos: MH370 debris A piece of aircraft debris found in Tanzania in June 2016 and transported to Australia. The country's Infrastructure and Transport minister said it was confirmed as coming from MH370 in September 2016. Hide Caption 6 of 7 Photos: MH370 debris A left outboard flap trailing edge section found on the island of Mauritius in May 2016. In October , it was confirmed as coming from MH370. Hide Caption 7 of 7

Theories

The research effort over the past three years has been herculean. Led by the Australian Transport Safety Bureau (ATSB), several reports have been compiled trying to eke out further details from the slivers of clues that exist -- especially the seven handshakes between the plane and Inmarsat satellite and the two unanswered satellite calls that were made from the ground to the plane.

Researchers have also examined various flight computations of potential routes, distances and end-of-flight scenarios -- such as which direction would the plane have fallen out of the sky once the fuel ran out and the engines stopped.

Throughout, there have been teams like the Independent Group -- a respected group of satellite and aviation experts -- whose own research has added to the understanding of what might have taken place. There have also been the critics, like Capt. Bryon Bailey in Australia , happy to tell investigators that their theories are wrong and they are looking in the wrong place.

Why call it off now?

Now the search is over and the plane has not been found.

The recent " First Principles Report " reviewing the search was definite in saying the area probably didn't contain the plane. The report went on to review the latest research and conclude "experts identified an area of approximately 25,000 square kilometers as the area with the highest probability of containing the wreckage of the aircraft."

The three governments involved in the search -- Australia, Malaysia and China -- have rejected that recommendation.

I find it bewildering that the governments have decided not to spend the extra money and search this new, smaller area. It is incomprehensible to me that their experts should have identified this potential new lead and the governments deny them money to continue.

This decision makes total nonsense of the Malaysian and Chinese governments' promise to do whatever is necessary to find MH370. The statement issued Tuesday calling off the underwater search doesn't even refer to the "First Principles Report."

Frankly, after three years of searching, it is a disgrace to suspend the effort now.

Search should continue

Why should the search go on? Because we know so little about what caused the plane's fate.

We know that the plane crashed into the southern Indian Ocean, because debris has been found and it can be tracked back to where the plane is believed to have gone down.

But that's about it. We don't know what happened on board the aircraft after 1:19 a.m. when the last words "goodnight Malaysian 370" were said from the cockpit. We don't know whether the captain was involved in the disappearance. We don't know why the transponder was switched off. We don't know why the Aircraft Communications Addressing and Reporting System was disabled. We don't know why a Malaysian air force radio operator didn't raise the alarm when he saw the plane flying back across Malaysia. We don't know what Indonesian radar saw (if anything) as the plane went around the country.

In short, we don't know whether the disappearance of MH370 was nefarious or mechanical. Which is why the decision to suspend the search is so wrong and should be reversed.