There is no official explanation for what happened exactly on Titan after Thanos left it, and prior to the crew arriving within the MCU. However, its likely one that can be easily explained within our own history, when a population gets desperate.
They simply warred with each other over resources until obliteration.
..One ongoing debate concerns the extent to which environmental abundance or scarcity contributes to underlying causes of conflict. Throughout history, countries have battled over natural resources....
...One natural resource that will be a likely source of major conflict is water as many of the world’s major rivers and underground aquifers cross national >boundaries....
The Titans are technologically very advanced, and they probably destroyed each other with very exotic and powerful weapons, which may have well caused all the planets physical anomalies.
If you read the comics, Thanos actually started a war on Titan and destroyed it himself, though it was rebuilt after a time.